Restoring authorship annotation for <orivej@yandex-team.ru>. Commit 2 of 2.

1 files changed, 2031 insertions, 2031 deletions

diff --git a/contrib/tools/python3/src/Lib/difflib.py b/contrib/tools/python3/src/Lib/difflib.py
index 384b48353b8..afd8a0c7c5b 100644
--- a/contrib/tools/python3/src/Lib/difflib.py
+++ b/contrib/tools/python3/src/Lib/difflib.py
@@ -1,2056 +1,2056 @@
-""" 
-Module difflib -- helpers for computing deltas between objects. 
- 
-Function get_close_matches(word, possibilities, n=3, cutoff=0.6): 
-    Use SequenceMatcher to return list of the best "good enough" matches. 
- 
-Function context_diff(a, b): 
-    For two lists of strings, return a delta in context diff format. 
- 
-Function ndiff(a, b): 
-    Return a delta: the difference between `a` and `b` (lists of strings). 
- 
-Function restore(delta, which): 
-    Return one of the two sequences that generated an ndiff delta. 
- 
-Function unified_diff(a, b): 
-    For two lists of strings, return a delta in unified diff format. 
- 
-Class SequenceMatcher: 
-    A flexible class for comparing pairs of sequences of any type. 
- 
-Class Differ: 
-    For producing human-readable deltas from sequences of lines of text. 
- 
-Class HtmlDiff: 
-    For producing HTML side by side comparison with change highlights. 
-""" 
- 
-__all__ = ['get_close_matches', 'ndiff', 'restore', 'SequenceMatcher', 
-           'Differ','IS_CHARACTER_JUNK', 'IS_LINE_JUNK', 'context_diff', 
-           'unified_diff', 'diff_bytes', 'HtmlDiff', 'Match'] 
- 
-from heapq import nlargest as _nlargest 
-from collections import namedtuple as _namedtuple 
+"""
+Module difflib -- helpers for computing deltas between objects.
+
+Function get_close_matches(word, possibilities, n=3, cutoff=0.6):
+    Use SequenceMatcher to return list of the best "good enough" matches.
+
+Function context_diff(a, b):
+    For two lists of strings, return a delta in context diff format.
+
+Function ndiff(a, b):
+    Return a delta: the difference between `a` and `b` (lists of strings).
+
+Function restore(delta, which):
+    Return one of the two sequences that generated an ndiff delta.
+
+Function unified_diff(a, b):
+    For two lists of strings, return a delta in unified diff format.
+
+Class SequenceMatcher:
+    A flexible class for comparing pairs of sequences of any type.
+
+Class Differ:
+    For producing human-readable deltas from sequences of lines of text.
+
+Class HtmlDiff:
+    For producing HTML side by side comparison with change highlights.
+"""
+
+__all__ = ['get_close_matches', 'ndiff', 'restore', 'SequenceMatcher',
+           'Differ','IS_CHARACTER_JUNK', 'IS_LINE_JUNK', 'context_diff',
+           'unified_diff', 'diff_bytes', 'HtmlDiff', 'Match']
+
+from heapq import nlargest as _nlargest
+from collections import namedtuple as _namedtuple
 from types import GenericAlias
- 
-Match = _namedtuple('Match', 'a b size') 
- 
-def _calculate_ratio(matches, length): 
-    if length: 
-        return 2.0 * matches / length 
-    return 1.0 
- 
-class SequenceMatcher: 
- 
-    """ 
-    SequenceMatcher is a flexible class for comparing pairs of sequences of 
-    any type, so long as the sequence elements are hashable.  The basic 
-    algorithm predates, and is a little fancier than, an algorithm 
-    published in the late 1980's by Ratcliff and Obershelp under the 
-    hyperbolic name "gestalt pattern matching".  The basic idea is to find 
-    the longest contiguous matching subsequence that contains no "junk" 
-    elements (R-O doesn't address junk).  The same idea is then applied 
-    recursively to the pieces of the sequences to the left and to the right 
-    of the matching subsequence.  This does not yield minimal edit 
-    sequences, but does tend to yield matches that "look right" to people. 
- 
-    SequenceMatcher tries to compute a "human-friendly diff" between two 
-    sequences.  Unlike e.g. UNIX(tm) diff, the fundamental notion is the 
-    longest *contiguous* & junk-free matching subsequence.  That's what 
-    catches peoples' eyes.  The Windows(tm) windiff has another interesting 
-    notion, pairing up elements that appear uniquely in each sequence. 
-    That, and the method here, appear to yield more intuitive difference 
-    reports than does diff.  This method appears to be the least vulnerable 
+
+Match = _namedtuple('Match', 'a b size')
+
+def _calculate_ratio(matches, length):
+    if length:
+        return 2.0 * matches / length
+    return 1.0
+
+class SequenceMatcher:
+
+    """
+    SequenceMatcher is a flexible class for comparing pairs of sequences of
+    any type, so long as the sequence elements are hashable.  The basic
+    algorithm predates, and is a little fancier than, an algorithm
+    published in the late 1980's by Ratcliff and Obershelp under the
+    hyperbolic name "gestalt pattern matching".  The basic idea is to find
+    the longest contiguous matching subsequence that contains no "junk"
+    elements (R-O doesn't address junk).  The same idea is then applied
+    recursively to the pieces of the sequences to the left and to the right
+    of the matching subsequence.  This does not yield minimal edit
+    sequences, but does tend to yield matches that "look right" to people.
+
+    SequenceMatcher tries to compute a "human-friendly diff" between two
+    sequences.  Unlike e.g. UNIX(tm) diff, the fundamental notion is the
+    longest *contiguous* & junk-free matching subsequence.  That's what
+    catches peoples' eyes.  The Windows(tm) windiff has another interesting
+    notion, pairing up elements that appear uniquely in each sequence.
+    That, and the method here, appear to yield more intuitive difference
+    reports than does diff.  This method appears to be the least vulnerable
     to syncing up on blocks of "junk lines", though (like blank lines in
-    ordinary text files, or maybe "<P>" lines in HTML files).  That may be 
-    because this is the only method of the 3 that has a *concept* of 
-    "junk" <wink>. 
- 
-    Example, comparing two strings, and considering blanks to be "junk": 
- 
-    >>> s = SequenceMatcher(lambda x: x == " ", 
-    ...                     "private Thread currentThread;", 
-    ...                     "private volatile Thread currentThread;") 
-    >>> 
- 
-    .ratio() returns a float in [0, 1], measuring the "similarity" of the 
-    sequences.  As a rule of thumb, a .ratio() value over 0.6 means the 
-    sequences are close matches: 
- 
-    >>> print(round(s.ratio(), 3)) 
-    0.866 
-    >>> 
- 
-    If you're only interested in where the sequences match, 
-    .get_matching_blocks() is handy: 
- 
-    >>> for block in s.get_matching_blocks(): 
-    ...     print("a[%d] and b[%d] match for %d elements" % block) 
-    a[0] and b[0] match for 8 elements 
-    a[8] and b[17] match for 21 elements 
-    a[29] and b[38] match for 0 elements 
- 
-    Note that the last tuple returned by .get_matching_blocks() is always a 
-    dummy, (len(a), len(b), 0), and this is the only case in which the last 
-    tuple element (number of elements matched) is 0. 
- 
-    If you want to know how to change the first sequence into the second, 
-    use .get_opcodes(): 
- 
-    >>> for opcode in s.get_opcodes(): 
-    ...     print("%6s a[%d:%d] b[%d:%d]" % opcode) 
-     equal a[0:8] b[0:8] 
-    insert a[8:8] b[8:17] 
-     equal a[8:29] b[17:38] 
- 
-    See the Differ class for a fancy human-friendly file differencer, which 
-    uses SequenceMatcher both to compare sequences of lines, and to compare 
-    sequences of characters within similar (near-matching) lines. 
- 
-    See also function get_close_matches() in this module, which shows how 
-    simple code building on SequenceMatcher can be used to do useful work. 
- 
-    Timing:  Basic R-O is cubic time worst case and quadratic time expected 
-    case.  SequenceMatcher is quadratic time for the worst case and has 
-    expected-case behavior dependent in a complicated way on how many 
-    elements the sequences have in common; best case time is linear. 
-    """ 
- 
-    def __init__(self, isjunk=None, a='', b='', autojunk=True): 
-        """Construct a SequenceMatcher. 
- 
-        Optional arg isjunk is None (the default), or a one-argument 
-        function that takes a sequence element and returns true iff the 
-        element is junk.  None is equivalent to passing "lambda x: 0", i.e. 
-        no elements are considered to be junk.  For example, pass 
-            lambda x: x in " \\t" 
-        if you're comparing lines as sequences of characters, and don't 
-        want to synch up on blanks or hard tabs. 
- 
-        Optional arg a is the first of two sequences to be compared.  By 
-        default, an empty string.  The elements of a must be hashable.  See 
-        also .set_seqs() and .set_seq1(). 
- 
-        Optional arg b is the second of two sequences to be compared.  By 
-        default, an empty string.  The elements of b must be hashable. See 
-        also .set_seqs() and .set_seq2(). 
- 
-        Optional arg autojunk should be set to False to disable the 
-        "automatic junk heuristic" that treats popular elements as junk 
-        (see module documentation for more information). 
-        """ 
- 
-        # Members: 
-        # a 
-        #      first sequence 
-        # b 
-        #      second sequence; differences are computed as "what do 
-        #      we need to do to 'a' to change it into 'b'?" 
-        # b2j 
-        #      for x in b, b2j[x] is a list of the indices (into b) 
-        #      at which x appears; junk and popular elements do not appear 
-        # fullbcount 
-        #      for x in b, fullbcount[x] == the number of times x 
-        #      appears in b; only materialized if really needed (used 
-        #      only for computing quick_ratio()) 
-        # matching_blocks 
-        #      a list of (i, j, k) triples, where a[i:i+k] == b[j:j+k]; 
-        #      ascending & non-overlapping in i and in j; terminated by 
-        #      a dummy (len(a), len(b), 0) sentinel 
-        # opcodes 
-        #      a list of (tag, i1, i2, j1, j2) tuples, where tag is 
-        #      one of 
-        #          'replace'   a[i1:i2] should be replaced by b[j1:j2] 
-        #          'delete'    a[i1:i2] should be deleted 
-        #          'insert'    b[j1:j2] should be inserted 
-        #          'equal'     a[i1:i2] == b[j1:j2] 
-        # isjunk 
-        #      a user-supplied function taking a sequence element and 
-        #      returning true iff the element is "junk" -- this has 
-        #      subtle but helpful effects on the algorithm, which I'll 
-        #      get around to writing up someday <0.9 wink>. 
-        #      DON'T USE!  Only __chain_b uses this.  Use "in self.bjunk". 
-        # bjunk 
-        #      the items in b for which isjunk is True. 
-        # bpopular 
-        #      nonjunk items in b treated as junk by the heuristic (if used). 
- 
-        self.isjunk = isjunk 
-        self.a = self.b = None 
-        self.autojunk = autojunk 
-        self.set_seqs(a, b) 
- 
-    def set_seqs(self, a, b): 
-        """Set the two sequences to be compared. 
- 
-        >>> s = SequenceMatcher() 
-        >>> s.set_seqs("abcd", "bcde") 
-        >>> s.ratio() 
-        0.75 
-        """ 
- 
-        self.set_seq1(a) 
-        self.set_seq2(b) 
- 
-    def set_seq1(self, a): 
-        """Set the first sequence to be compared. 
- 
-        The second sequence to be compared is not changed. 
- 
-        >>> s = SequenceMatcher(None, "abcd", "bcde") 
-        >>> s.ratio() 
-        0.75 
-        >>> s.set_seq1("bcde") 
-        >>> s.ratio() 
-        1.0 
-        >>> 
- 
-        SequenceMatcher computes and caches detailed information about the 
-        second sequence, so if you want to compare one sequence S against 
-        many sequences, use .set_seq2(S) once and call .set_seq1(x) 
-        repeatedly for each of the other sequences. 
- 
-        See also set_seqs() and set_seq2(). 
-        """ 
- 
-        if a is self.a: 
-            return 
-        self.a = a 
-        self.matching_blocks = self.opcodes = None 
- 
-    def set_seq2(self, b): 
-        """Set the second sequence to be compared. 
- 
-        The first sequence to be compared is not changed. 
- 
-        >>> s = SequenceMatcher(None, "abcd", "bcde") 
-        >>> s.ratio() 
-        0.75 
-        >>> s.set_seq2("abcd") 
-        >>> s.ratio() 
-        1.0 
-        >>> 
- 
-        SequenceMatcher computes and caches detailed information about the 
-        second sequence, so if you want to compare one sequence S against 
-        many sequences, use .set_seq2(S) once and call .set_seq1(x) 
-        repeatedly for each of the other sequences. 
- 
-        See also set_seqs() and set_seq1(). 
-        """ 
- 
-        if b is self.b: 
-            return 
-        self.b = b 
-        self.matching_blocks = self.opcodes = None 
-        self.fullbcount = None 
-        self.__chain_b() 
- 
-    # For each element x in b, set b2j[x] to a list of the indices in 
-    # b where x appears; the indices are in increasing order; note that 
-    # the number of times x appears in b is len(b2j[x]) ... 
-    # when self.isjunk is defined, junk elements don't show up in this 
-    # map at all, which stops the central find_longest_match method 
-    # from starting any matching block at a junk element ... 
-    # b2j also does not contain entries for "popular" elements, meaning 
-    # elements that account for more than 1 + 1% of the total elements, and 
-    # when the sequence is reasonably large (>= 200 elements); this can 
-    # be viewed as an adaptive notion of semi-junk, and yields an enormous 
-    # speedup when, e.g., comparing program files with hundreds of 
-    # instances of "return NULL;" ... 
-    # note that this is only called when b changes; so for cross-product 
-    # kinds of matches, it's best to call set_seq2 once, then set_seq1 
-    # repeatedly 
- 
-    def __chain_b(self): 
-        # Because isjunk is a user-defined (not C) function, and we test 
-        # for junk a LOT, it's important to minimize the number of calls. 
-        # Before the tricks described here, __chain_b was by far the most 
-        # time-consuming routine in the whole module!  If anyone sees 
-        # Jim Roskind, thank him again for profile.py -- I never would 
-        # have guessed that. 
-        # The first trick is to build b2j ignoring the possibility 
-        # of junk.  I.e., we don't call isjunk at all yet.  Throwing 
-        # out the junk later is much cheaper than building b2j "right" 
-        # from the start. 
-        b = self.b 
-        self.b2j = b2j = {} 
- 
-        for i, elt in enumerate(b): 
-            indices = b2j.setdefault(elt, []) 
-            indices.append(i) 
- 
-        # Purge junk elements 
-        self.bjunk = junk = set() 
-        isjunk = self.isjunk 
-        if isjunk: 
-            for elt in b2j.keys(): 
-                if isjunk(elt): 
-                    junk.add(elt) 
-            for elt in junk: # separate loop avoids separate list of keys 
-                del b2j[elt] 
- 
-        # Purge popular elements that are not junk 
-        self.bpopular = popular = set() 
-        n = len(b) 
-        if self.autojunk and n >= 200: 
-            ntest = n // 100 + 1 
-            for elt, idxs in b2j.items(): 
-                if len(idxs) > ntest: 
-                    popular.add(elt) 
-            for elt in popular: # ditto; as fast for 1% deletion 
-                del b2j[elt] 
- 
+    ordinary text files, or maybe "<P>" lines in HTML files).  That may be
+    because this is the only method of the 3 that has a *concept* of
+    "junk" <wink>.
+
+    Example, comparing two strings, and considering blanks to be "junk":
+
+    >>> s = SequenceMatcher(lambda x: x == " ",
+    ...                     "private Thread currentThread;",
+    ...                     "private volatile Thread currentThread;")
+    >>>
+
+    .ratio() returns a float in [0, 1], measuring the "similarity" of the
+    sequences.  As a rule of thumb, a .ratio() value over 0.6 means the
+    sequences are close matches:
+
+    >>> print(round(s.ratio(), 3))
+    0.866
+    >>>
+
+    If you're only interested in where the sequences match,
+    .get_matching_blocks() is handy:
+
+    >>> for block in s.get_matching_blocks():
+    ...     print("a[%d] and b[%d] match for %d elements" % block)
+    a[0] and b[0] match for 8 elements
+    a[8] and b[17] match for 21 elements
+    a[29] and b[38] match for 0 elements
+
+    Note that the last tuple returned by .get_matching_blocks() is always a
+    dummy, (len(a), len(b), 0), and this is the only case in which the last
+    tuple element (number of elements matched) is 0.
+
+    If you want to know how to change the first sequence into the second,
+    use .get_opcodes():
+
+    >>> for opcode in s.get_opcodes():
+    ...     print("%6s a[%d:%d] b[%d:%d]" % opcode)
+     equal a[0:8] b[0:8]
+    insert a[8:8] b[8:17]
+     equal a[8:29] b[17:38]
+
+    See the Differ class for a fancy human-friendly file differencer, which
+    uses SequenceMatcher both to compare sequences of lines, and to compare
+    sequences of characters within similar (near-matching) lines.
+
+    See also function get_close_matches() in this module, which shows how
+    simple code building on SequenceMatcher can be used to do useful work.
+
+    Timing:  Basic R-O is cubic time worst case and quadratic time expected
+    case.  SequenceMatcher is quadratic time for the worst case and has
+    expected-case behavior dependent in a complicated way on how many
+    elements the sequences have in common; best case time is linear.
+    """
+
+    def __init__(self, isjunk=None, a='', b='', autojunk=True):
+        """Construct a SequenceMatcher.
+
+        Optional arg isjunk is None (the default), or a one-argument
+        function that takes a sequence element and returns true iff the
+        element is junk.  None is equivalent to passing "lambda x: 0", i.e.
+        no elements are considered to be junk.  For example, pass
+            lambda x: x in " \\t"
+        if you're comparing lines as sequences of characters, and don't
+        want to synch up on blanks or hard tabs.
+
+        Optional arg a is the first of two sequences to be compared.  By
+        default, an empty string.  The elements of a must be hashable.  See
+        also .set_seqs() and .set_seq1().
+
+        Optional arg b is the second of two sequences to be compared.  By
+        default, an empty string.  The elements of b must be hashable. See
+        also .set_seqs() and .set_seq2().
+
+        Optional arg autojunk should be set to False to disable the
+        "automatic junk heuristic" that treats popular elements as junk
+        (see module documentation for more information).
+        """
+
+        # Members:
+        # a
+        #      first sequence
+        # b
+        #      second sequence; differences are computed as "what do
+        #      we need to do to 'a' to change it into 'b'?"
+        # b2j
+        #      for x in b, b2j[x] is a list of the indices (into b)
+        #      at which x appears; junk and popular elements do not appear
+        # fullbcount
+        #      for x in b, fullbcount[x] == the number of times x
+        #      appears in b; only materialized if really needed (used
+        #      only for computing quick_ratio())
+        # matching_blocks
+        #      a list of (i, j, k) triples, where a[i:i+k] == b[j:j+k];
+        #      ascending & non-overlapping in i and in j; terminated by
+        #      a dummy (len(a), len(b), 0) sentinel
+        # opcodes
+        #      a list of (tag, i1, i2, j1, j2) tuples, where tag is
+        #      one of
+        #          'replace'   a[i1:i2] should be replaced by b[j1:j2]
+        #          'delete'    a[i1:i2] should be deleted
+        #          'insert'    b[j1:j2] should be inserted
+        #          'equal'     a[i1:i2] == b[j1:j2]
+        # isjunk
+        #      a user-supplied function taking a sequence element and
+        #      returning true iff the element is "junk" -- this has
+        #      subtle but helpful effects on the algorithm, which I'll
+        #      get around to writing up someday <0.9 wink>.
+        #      DON'T USE!  Only __chain_b uses this.  Use "in self.bjunk".
+        # bjunk
+        #      the items in b for which isjunk is True.
+        # bpopular
+        #      nonjunk items in b treated as junk by the heuristic (if used).
+
+        self.isjunk = isjunk
+        self.a = self.b = None
+        self.autojunk = autojunk
+        self.set_seqs(a, b)
+
+    def set_seqs(self, a, b):
+        """Set the two sequences to be compared.
+
+        >>> s = SequenceMatcher()
+        >>> s.set_seqs("abcd", "bcde")
+        >>> s.ratio()
+        0.75
+        """
+
+        self.set_seq1(a)
+        self.set_seq2(b)
+
+    def set_seq1(self, a):
+        """Set the first sequence to be compared.
+
+        The second sequence to be compared is not changed.
+
+        >>> s = SequenceMatcher(None, "abcd", "bcde")
+        >>> s.ratio()
+        0.75
+        >>> s.set_seq1("bcde")
+        >>> s.ratio()
+        1.0
+        >>>
+
+        SequenceMatcher computes and caches detailed information about the
+        second sequence, so if you want to compare one sequence S against
+        many sequences, use .set_seq2(S) once and call .set_seq1(x)
+        repeatedly for each of the other sequences.
+
+        See also set_seqs() and set_seq2().
+        """
+
+        if a is self.a:
+            return
+        self.a = a
+        self.matching_blocks = self.opcodes = None
+
+    def set_seq2(self, b):
+        """Set the second sequence to be compared.
+
+        The first sequence to be compared is not changed.
+
+        >>> s = SequenceMatcher(None, "abcd", "bcde")
+        >>> s.ratio()
+        0.75
+        >>> s.set_seq2("abcd")
+        >>> s.ratio()
+        1.0
+        >>>
+
+        SequenceMatcher computes and caches detailed information about the
+        second sequence, so if you want to compare one sequence S against
+        many sequences, use .set_seq2(S) once and call .set_seq1(x)
+        repeatedly for each of the other sequences.
+
+        See also set_seqs() and set_seq1().
+        """
+
+        if b is self.b:
+            return
+        self.b = b
+        self.matching_blocks = self.opcodes = None
+        self.fullbcount = None
+        self.__chain_b()
+
+    # For each element x in b, set b2j[x] to a list of the indices in
+    # b where x appears; the indices are in increasing order; note that
+    # the number of times x appears in b is len(b2j[x]) ...
+    # when self.isjunk is defined, junk elements don't show up in this
+    # map at all, which stops the central find_longest_match method
+    # from starting any matching block at a junk element ...
+    # b2j also does not contain entries for "popular" elements, meaning
+    # elements that account for more than 1 + 1% of the total elements, and
+    # when the sequence is reasonably large (>= 200 elements); this can
+    # be viewed as an adaptive notion of semi-junk, and yields an enormous
+    # speedup when, e.g., comparing program files with hundreds of
+    # instances of "return NULL;" ...
+    # note that this is only called when b changes; so for cross-product
+    # kinds of matches, it's best to call set_seq2 once, then set_seq1
+    # repeatedly
+
+    def __chain_b(self):
+        # Because isjunk is a user-defined (not C) function, and we test
+        # for junk a LOT, it's important to minimize the number of calls.
+        # Before the tricks described here, __chain_b was by far the most
+        # time-consuming routine in the whole module!  If anyone sees
+        # Jim Roskind, thank him again for profile.py -- I never would
+        # have guessed that.
+        # The first trick is to build b2j ignoring the possibility
+        # of junk.  I.e., we don't call isjunk at all yet.  Throwing
+        # out the junk later is much cheaper than building b2j "right"
+        # from the start.
+        b = self.b
+        self.b2j = b2j = {}
+
+        for i, elt in enumerate(b):
+            indices = b2j.setdefault(elt, [])
+            indices.append(i)
+
+        # Purge junk elements
+        self.bjunk = junk = set()
+        isjunk = self.isjunk
+        if isjunk:
+            for elt in b2j.keys():
+                if isjunk(elt):
+                    junk.add(elt)
+            for elt in junk: # separate loop avoids separate list of keys
+                del b2j[elt]
+
+        # Purge popular elements that are not junk
+        self.bpopular = popular = set()
+        n = len(b)
+        if self.autojunk and n >= 200:
+            ntest = n // 100 + 1
+            for elt, idxs in b2j.items():
+                if len(idxs) > ntest:
+                    popular.add(elt)
+            for elt in popular: # ditto; as fast for 1% deletion
+                del b2j[elt]
+
     def find_longest_match(self, alo=0, ahi=None, blo=0, bhi=None):
-        """Find longest matching block in a[alo:ahi] and b[blo:bhi]. 
- 
+        """Find longest matching block in a[alo:ahi] and b[blo:bhi].
+
         By default it will find the longest match in the entirety of a and b.
 
-        If isjunk is not defined: 
- 
-        Return (i,j,k) such that a[i:i+k] is equal to b[j:j+k], where 
-            alo <= i <= i+k <= ahi 
-            blo <= j <= j+k <= bhi 
-        and for all (i',j',k') meeting those conditions, 
-            k >= k' 
-            i <= i' 
-            and if i == i', j <= j' 
- 
-        In other words, of all maximal matching blocks, return one that 
-        starts earliest in a, and of all those maximal matching blocks that 
-        start earliest in a, return the one that starts earliest in b. 
- 
-        >>> s = SequenceMatcher(None, " abcd", "abcd abcd") 
-        >>> s.find_longest_match(0, 5, 0, 9) 
-        Match(a=0, b=4, size=5) 
- 
-        If isjunk is defined, first the longest matching block is 
-        determined as above, but with the additional restriction that no 
-        junk element appears in the block.  Then that block is extended as 
-        far as possible by matching (only) junk elements on both sides.  So 
-        the resulting block never matches on junk except as identical junk 
-        happens to be adjacent to an "interesting" match. 
- 
-        Here's the same example as before, but considering blanks to be 
-        junk.  That prevents " abcd" from matching the " abcd" at the tail 
-        end of the second sequence directly.  Instead only the "abcd" can 
-        match, and matches the leftmost "abcd" in the second sequence: 
- 
-        >>> s = SequenceMatcher(lambda x: x==" ", " abcd", "abcd abcd") 
-        >>> s.find_longest_match(0, 5, 0, 9) 
-        Match(a=1, b=0, size=4) 
- 
-        If no blocks match, return (alo, blo, 0). 
- 
-        >>> s = SequenceMatcher(None, "ab", "c") 
-        >>> s.find_longest_match(0, 2, 0, 1) 
-        Match(a=0, b=0, size=0) 
-        """ 
- 
-        # CAUTION:  stripping common prefix or suffix would be incorrect. 
-        # E.g., 
-        #    ab 
-        #    acab 
-        # Longest matching block is "ab", but if common prefix is 
-        # stripped, it's "a" (tied with "b").  UNIX(tm) diff does so 
-        # strip, so ends up claiming that ab is changed to acab by 
-        # inserting "ca" in the middle.  That's minimal but unintuitive: 
-        # "it's obvious" that someone inserted "ac" at the front. 
-        # Windiff ends up at the same place as diff, but by pairing up 
-        # the unique 'b's and then matching the first two 'a's. 
- 
-        a, b, b2j, isbjunk = self.a, self.b, self.b2j, self.bjunk.__contains__ 
+        If isjunk is not defined:
+
+        Return (i,j,k) such that a[i:i+k] is equal to b[j:j+k], where
+            alo <= i <= i+k <= ahi
+            blo <= j <= j+k <= bhi
+        and for all (i',j',k') meeting those conditions,
+            k >= k'
+            i <= i'
+            and if i == i', j <= j'
+
+        In other words, of all maximal matching blocks, return one that
+        starts earliest in a, and of all those maximal matching blocks that
+        start earliest in a, return the one that starts earliest in b.
+
+        >>> s = SequenceMatcher(None, " abcd", "abcd abcd")
+        >>> s.find_longest_match(0, 5, 0, 9)
+        Match(a=0, b=4, size=5)
+
+        If isjunk is defined, first the longest matching block is
+        determined as above, but with the additional restriction that no
+        junk element appears in the block.  Then that block is extended as
+        far as possible by matching (only) junk elements on both sides.  So
+        the resulting block never matches on junk except as identical junk
+        happens to be adjacent to an "interesting" match.
+
+        Here's the same example as before, but considering blanks to be
+        junk.  That prevents " abcd" from matching the " abcd" at the tail
+        end of the second sequence directly.  Instead only the "abcd" can
+        match, and matches the leftmost "abcd" in the second sequence:
+
+        >>> s = SequenceMatcher(lambda x: x==" ", " abcd", "abcd abcd")
+        >>> s.find_longest_match(0, 5, 0, 9)
+        Match(a=1, b=0, size=4)
+
+        If no blocks match, return (alo, blo, 0).
+
+        >>> s = SequenceMatcher(None, "ab", "c")
+        >>> s.find_longest_match(0, 2, 0, 1)
+        Match(a=0, b=0, size=0)
+        """
+
+        # CAUTION:  stripping common prefix or suffix would be incorrect.
+        # E.g.,
+        #    ab
+        #    acab
+        # Longest matching block is "ab", but if common prefix is
+        # stripped, it's "a" (tied with "b").  UNIX(tm) diff does so
+        # strip, so ends up claiming that ab is changed to acab by
+        # inserting "ca" in the middle.  That's minimal but unintuitive:
+        # "it's obvious" that someone inserted "ac" at the front.
+        # Windiff ends up at the same place as diff, but by pairing up
+        # the unique 'b's and then matching the first two 'a's.
+
+        a, b, b2j, isbjunk = self.a, self.b, self.b2j, self.bjunk.__contains__
         if ahi is None:
             ahi = len(a)
         if bhi is None:
             bhi = len(b)
-        besti, bestj, bestsize = alo, blo, 0 
-        # find longest junk-free match 
-        # during an iteration of the loop, j2len[j] = length of longest 
-        # junk-free match ending with a[i-1] and b[j] 
-        j2len = {} 
-        nothing = [] 
-        for i in range(alo, ahi): 
-            # look at all instances of a[i] in b; note that because 
-            # b2j has no junk keys, the loop is skipped if a[i] is junk 
-            j2lenget = j2len.get 
-            newj2len = {} 
-            for j in b2j.get(a[i], nothing): 
-                # a[i] matches b[j] 
-                if j < blo: 
-                    continue 
-                if j >= bhi: 
-                    break 
-                k = newj2len[j] = j2lenget(j-1, 0) + 1 
-                if k > bestsize: 
-                    besti, bestj, bestsize = i-k+1, j-k+1, k 
-            j2len = newj2len 
- 
-        # Extend the best by non-junk elements on each end.  In particular, 
-        # "popular" non-junk elements aren't in b2j, which greatly speeds 
-        # the inner loop above, but also means "the best" match so far 
-        # doesn't contain any junk *or* popular non-junk elements. 
-        while besti > alo and bestj > blo and \ 
-              not isbjunk(b[bestj-1]) and \ 
-              a[besti-1] == b[bestj-1]: 
-            besti, bestj, bestsize = besti-1, bestj-1, bestsize+1 
-        while besti+bestsize < ahi and bestj+bestsize < bhi and \ 
-              not isbjunk(b[bestj+bestsize]) and \ 
-              a[besti+bestsize] == b[bestj+bestsize]: 
-            bestsize += 1 
- 
-        # Now that we have a wholly interesting match (albeit possibly 
-        # empty!), we may as well suck up the matching junk on each 
-        # side of it too.  Can't think of a good reason not to, and it 
-        # saves post-processing the (possibly considerable) expense of 
-        # figuring out what to do with it.  In the case of an empty 
-        # interesting match, this is clearly the right thing to do, 
-        # because no other kind of match is possible in the regions. 
-        while besti > alo and bestj > blo and \ 
-              isbjunk(b[bestj-1]) and \ 
-              a[besti-1] == b[bestj-1]: 
-            besti, bestj, bestsize = besti-1, bestj-1, bestsize+1 
-        while besti+bestsize < ahi and bestj+bestsize < bhi and \ 
-              isbjunk(b[bestj+bestsize]) and \ 
-              a[besti+bestsize] == b[bestj+bestsize]: 
-            bestsize = bestsize + 1 
- 
-        return Match(besti, bestj, bestsize) 
- 
-    def get_matching_blocks(self): 
-        """Return list of triples describing matching subsequences. 
- 
-        Each triple is of the form (i, j, n), and means that 
-        a[i:i+n] == b[j:j+n].  The triples are monotonically increasing in 
-        i and in j.  New in Python 2.5, it's also guaranteed that if 
-        (i, j, n) and (i', j', n') are adjacent triples in the list, and 
-        the second is not the last triple in the list, then i+n != i' or 
-        j+n != j'.  IOW, adjacent triples never describe adjacent equal 
-        blocks. 
- 
-        The last triple is a dummy, (len(a), len(b), 0), and is the only 
-        triple with n==0. 
- 
-        >>> s = SequenceMatcher(None, "abxcd", "abcd") 
-        >>> list(s.get_matching_blocks()) 
-        [Match(a=0, b=0, size=2), Match(a=3, b=2, size=2), Match(a=5, b=4, size=0)] 
-        """ 
- 
-        if self.matching_blocks is not None: 
-            return self.matching_blocks 
-        la, lb = len(self.a), len(self.b) 
- 
-        # This is most naturally expressed as a recursive algorithm, but 
-        # at least one user bumped into extreme use cases that exceeded 
-        # the recursion limit on their box.  So, now we maintain a list 
-        # ('queue`) of blocks we still need to look at, and append partial 
-        # results to `matching_blocks` in a loop; the matches are sorted 
-        # at the end. 
-        queue = [(0, la, 0, lb)] 
-        matching_blocks = [] 
-        while queue: 
-            alo, ahi, blo, bhi = queue.pop() 
-            i, j, k = x = self.find_longest_match(alo, ahi, blo, bhi) 
-            # a[alo:i] vs b[blo:j] unknown 
-            # a[i:i+k] same as b[j:j+k] 
-            # a[i+k:ahi] vs b[j+k:bhi] unknown 
-            if k:   # if k is 0, there was no matching block 
-                matching_blocks.append(x) 
-                if alo < i and blo < j: 
-                    queue.append((alo, i, blo, j)) 
-                if i+k < ahi and j+k < bhi: 
-                    queue.append((i+k, ahi, j+k, bhi)) 
-        matching_blocks.sort() 
- 
-        # It's possible that we have adjacent equal blocks in the 
-        # matching_blocks list now.  Starting with 2.5, this code was added 
-        # to collapse them. 
-        i1 = j1 = k1 = 0 
-        non_adjacent = [] 
-        for i2, j2, k2 in matching_blocks: 
-            # Is this block adjacent to i1, j1, k1? 
-            if i1 + k1 == i2 and j1 + k1 == j2: 
-                # Yes, so collapse them -- this just increases the length of 
-                # the first block by the length of the second, and the first 
-                # block so lengthened remains the block to compare against. 
-                k1 += k2 
-            else: 
-                # Not adjacent.  Remember the first block (k1==0 means it's 
-                # the dummy we started with), and make the second block the 
-                # new block to compare against. 
-                if k1: 
-                    non_adjacent.append((i1, j1, k1)) 
-                i1, j1, k1 = i2, j2, k2 
-        if k1: 
-            non_adjacent.append((i1, j1, k1)) 
- 
-        non_adjacent.append( (la, lb, 0) ) 
-        self.matching_blocks = list(map(Match._make, non_adjacent)) 
-        return self.matching_blocks 
- 
-    def get_opcodes(self): 
-        """Return list of 5-tuples describing how to turn a into b. 
- 
-        Each tuple is of the form (tag, i1, i2, j1, j2).  The first tuple 
-        has i1 == j1 == 0, and remaining tuples have i1 == the i2 from the 
-        tuple preceding it, and likewise for j1 == the previous j2. 
- 
-        The tags are strings, with these meanings: 
- 
-        'replace':  a[i1:i2] should be replaced by b[j1:j2] 
-        'delete':   a[i1:i2] should be deleted. 
-                    Note that j1==j2 in this case. 
-        'insert':   b[j1:j2] should be inserted at a[i1:i1]. 
-                    Note that i1==i2 in this case. 
-        'equal':    a[i1:i2] == b[j1:j2] 
- 
-        >>> a = "qabxcd" 
-        >>> b = "abycdf" 
-        >>> s = SequenceMatcher(None, a, b) 
-        >>> for tag, i1, i2, j1, j2 in s.get_opcodes(): 
-        ...    print(("%7s a[%d:%d] (%s) b[%d:%d] (%s)" % 
-        ...           (tag, i1, i2, a[i1:i2], j1, j2, b[j1:j2]))) 
-         delete a[0:1] (q) b[0:0] () 
-          equal a[1:3] (ab) b[0:2] (ab) 
-        replace a[3:4] (x) b[2:3] (y) 
-          equal a[4:6] (cd) b[3:5] (cd) 
-         insert a[6:6] () b[5:6] (f) 
-        """ 
- 
-        if self.opcodes is not None: 
-            return self.opcodes 
-        i = j = 0 
-        self.opcodes = answer = [] 
-        for ai, bj, size in self.get_matching_blocks(): 
-            # invariant:  we've pumped out correct diffs to change 
-            # a[:i] into b[:j], and the next matching block is 
-            # a[ai:ai+size] == b[bj:bj+size].  So we need to pump 
-            # out a diff to change a[i:ai] into b[j:bj], pump out 
-            # the matching block, and move (i,j) beyond the match 
-            tag = '' 
-            if i < ai and j < bj: 
-                tag = 'replace' 
-            elif i < ai: 
-                tag = 'delete' 
-            elif j < bj: 
-                tag = 'insert' 
-            if tag: 
-                answer.append( (tag, i, ai, j, bj) ) 
-            i, j = ai+size, bj+size 
-            # the list of matching blocks is terminated by a 
-            # sentinel with size 0 
-            if size: 
-                answer.append( ('equal', ai, i, bj, j) ) 
-        return answer 
- 
-    def get_grouped_opcodes(self, n=3): 
-        """ Isolate change clusters by eliminating ranges with no changes. 
- 
-        Return a generator of groups with up to n lines of context. 
-        Each group is in the same format as returned by get_opcodes(). 
- 
-        >>> from pprint import pprint 
-        >>> a = list(map(str, range(1,40))) 
-        >>> b = a[:] 
-        >>> b[8:8] = ['i']     # Make an insertion 
-        >>> b[20] += 'x'       # Make a replacement 
-        >>> b[23:28] = []      # Make a deletion 
-        >>> b[30] += 'y'       # Make another replacement 
-        >>> pprint(list(SequenceMatcher(None,a,b).get_grouped_opcodes())) 
-        [[('equal', 5, 8, 5, 8), ('insert', 8, 8, 8, 9), ('equal', 8, 11, 9, 12)], 
-         [('equal', 16, 19, 17, 20), 
-          ('replace', 19, 20, 20, 21), 
-          ('equal', 20, 22, 21, 23), 
-          ('delete', 22, 27, 23, 23), 
-          ('equal', 27, 30, 23, 26)], 
-         [('equal', 31, 34, 27, 30), 
-          ('replace', 34, 35, 30, 31), 
-          ('equal', 35, 38, 31, 34)]] 
-        """ 
- 
-        codes = self.get_opcodes() 
-        if not codes: 
-            codes = [("equal", 0, 1, 0, 1)] 
-        # Fixup leading and trailing groups if they show no changes. 
-        if codes[0][0] == 'equal': 
-            tag, i1, i2, j1, j2 = codes[0] 
-            codes[0] = tag, max(i1, i2-n), i2, max(j1, j2-n), j2 
-        if codes[-1][0] == 'equal': 
-            tag, i1, i2, j1, j2 = codes[-1] 
-            codes[-1] = tag, i1, min(i2, i1+n), j1, min(j2, j1+n) 
- 
-        nn = n + n 
-        group = [] 
-        for tag, i1, i2, j1, j2 in codes: 
-            # End the current group and start a new one whenever 
-            # there is a large range with no changes. 
-            if tag == 'equal' and i2-i1 > nn: 
-                group.append((tag, i1, min(i2, i1+n), j1, min(j2, j1+n))) 
-                yield group 
-                group = [] 
-                i1, j1 = max(i1, i2-n), max(j1, j2-n) 
-            group.append((tag, i1, i2, j1 ,j2)) 
-        if group and not (len(group)==1 and group[0][0] == 'equal'): 
-            yield group 
- 
-    def ratio(self): 
-        """Return a measure of the sequences' similarity (float in [0,1]). 
- 
-        Where T is the total number of elements in both sequences, and 
-        M is the number of matches, this is 2.0*M / T. 
-        Note that this is 1 if the sequences are identical, and 0 if 
-        they have nothing in common. 
- 
-        .ratio() is expensive to compute if you haven't already computed 
-        .get_matching_blocks() or .get_opcodes(), in which case you may 
-        want to try .quick_ratio() or .real_quick_ratio() first to get an 
-        upper bound. 
- 
-        >>> s = SequenceMatcher(None, "abcd", "bcde") 
-        >>> s.ratio() 
-        0.75 
-        >>> s.quick_ratio() 
-        0.75 
-        >>> s.real_quick_ratio() 
-        1.0 
-        """ 
- 
-        matches = sum(triple[-1] for triple in self.get_matching_blocks()) 
-        return _calculate_ratio(matches, len(self.a) + len(self.b)) 
- 
-    def quick_ratio(self): 
-        """Return an upper bound on ratio() relatively quickly. 
- 
-        This isn't defined beyond that it is an upper bound on .ratio(), and 
-        is faster to compute. 
-        """ 
- 
-        # viewing a and b as multisets, set matches to the cardinality 
-        # of their intersection; this counts the number of matches 
-        # without regard to order, so is clearly an upper bound 
-        if self.fullbcount is None: 
-            self.fullbcount = fullbcount = {} 
-            for elt in self.b: 
-                fullbcount[elt] = fullbcount.get(elt, 0) + 1 
-        fullbcount = self.fullbcount 
-        # avail[x] is the number of times x appears in 'b' less the 
-        # number of times we've seen it in 'a' so far ... kinda 
-        avail = {} 
-        availhas, matches = avail.__contains__, 0 
-        for elt in self.a: 
-            if availhas(elt): 
-                numb = avail[elt] 
-            else: 
-                numb = fullbcount.get(elt, 0) 
-            avail[elt] = numb - 1 
-            if numb > 0: 
-                matches = matches + 1 
-        return _calculate_ratio(matches, len(self.a) + len(self.b)) 
- 
-    def real_quick_ratio(self): 
-        """Return an upper bound on ratio() very quickly. 
- 
-        This isn't defined beyond that it is an upper bound on .ratio(), and 
-        is faster to compute than either .ratio() or .quick_ratio(). 
-        """ 
- 
-        la, lb = len(self.a), len(self.b) 
-        # can't have more matches than the number of elements in the 
-        # shorter sequence 
-        return _calculate_ratio(min(la, lb), la + lb) 
- 
+        besti, bestj, bestsize = alo, blo, 0
+        # find longest junk-free match
+        # during an iteration of the loop, j2len[j] = length of longest
+        # junk-free match ending with a[i-1] and b[j]
+        j2len = {}
+        nothing = []
+        for i in range(alo, ahi):
+            # look at all instances of a[i] in b; note that because
+            # b2j has no junk keys, the loop is skipped if a[i] is junk
+            j2lenget = j2len.get
+            newj2len = {}
+            for j in b2j.get(a[i], nothing):
+                # a[i] matches b[j]
+                if j < blo:
+                    continue
+                if j >= bhi:
+                    break
+                k = newj2len[j] = j2lenget(j-1, 0) + 1
+                if k > bestsize:
+                    besti, bestj, bestsize = i-k+1, j-k+1, k
+            j2len = newj2len
+
+        # Extend the best by non-junk elements on each end.  In particular,
+        # "popular" non-junk elements aren't in b2j, which greatly speeds
+        # the inner loop above, but also means "the best" match so far
+        # doesn't contain any junk *or* popular non-junk elements.
+        while besti > alo and bestj > blo and \
+              not isbjunk(b[bestj-1]) and \
+              a[besti-1] == b[bestj-1]:
+            besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
+        while besti+bestsize < ahi and bestj+bestsize < bhi and \
+              not isbjunk(b[bestj+bestsize]) and \
+              a[besti+bestsize] == b[bestj+bestsize]:
+            bestsize += 1
+
+        # Now that we have a wholly interesting match (albeit possibly
+        # empty!), we may as well suck up the matching junk on each
+        # side of it too.  Can't think of a good reason not to, and it
+        # saves post-processing the (possibly considerable) expense of
+        # figuring out what to do with it.  In the case of an empty
+        # interesting match, this is clearly the right thing to do,
+        # because no other kind of match is possible in the regions.
+        while besti > alo and bestj > blo and \
+              isbjunk(b[bestj-1]) and \
+              a[besti-1] == b[bestj-1]:
+            besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
+        while besti+bestsize < ahi and bestj+bestsize < bhi and \
+              isbjunk(b[bestj+bestsize]) and \
+              a[besti+bestsize] == b[bestj+bestsize]:
+            bestsize = bestsize + 1
+
+        return Match(besti, bestj, bestsize)
+
+    def get_matching_blocks(self):
+        """Return list of triples describing matching subsequences.
+
+        Each triple is of the form (i, j, n), and means that
+        a[i:i+n] == b[j:j+n].  The triples are monotonically increasing in
+        i and in j.  New in Python 2.5, it's also guaranteed that if
+        (i, j, n) and (i', j', n') are adjacent triples in the list, and
+        the second is not the last triple in the list, then i+n != i' or
+        j+n != j'.  IOW, adjacent triples never describe adjacent equal
+        blocks.
+
+        The last triple is a dummy, (len(a), len(b), 0), and is the only
+        triple with n==0.
+
+        >>> s = SequenceMatcher(None, "abxcd", "abcd")
+        >>> list(s.get_matching_blocks())
+        [Match(a=0, b=0, size=2), Match(a=3, b=2, size=2), Match(a=5, b=4, size=0)]
+        """
+
+        if self.matching_blocks is not None:
+            return self.matching_blocks
+        la, lb = len(self.a), len(self.b)
+
+        # This is most naturally expressed as a recursive algorithm, but
+        # at least one user bumped into extreme use cases that exceeded
+        # the recursion limit on their box.  So, now we maintain a list
+        # ('queue`) of blocks we still need to look at, and append partial
+        # results to `matching_blocks` in a loop; the matches are sorted
+        # at the end.
+        queue = [(0, la, 0, lb)]
+        matching_blocks = []
+        while queue:
+            alo, ahi, blo, bhi = queue.pop()
+            i, j, k = x = self.find_longest_match(alo, ahi, blo, bhi)
+            # a[alo:i] vs b[blo:j] unknown
+            # a[i:i+k] same as b[j:j+k]
+            # a[i+k:ahi] vs b[j+k:bhi] unknown
+            if k:   # if k is 0, there was no matching block
+                matching_blocks.append(x)
+                if alo < i and blo < j:
+                    queue.append((alo, i, blo, j))
+                if i+k < ahi and j+k < bhi:
+                    queue.append((i+k, ahi, j+k, bhi))
+        matching_blocks.sort()
+
+        # It's possible that we have adjacent equal blocks in the
+        # matching_blocks list now.  Starting with 2.5, this code was added
+        # to collapse them.
+        i1 = j1 = k1 = 0
+        non_adjacent = []
+        for i2, j2, k2 in matching_blocks:
+            # Is this block adjacent to i1, j1, k1?
+            if i1 + k1 == i2 and j1 + k1 == j2:
+                # Yes, so collapse them -- this just increases the length of
+                # the first block by the length of the second, and the first
+                # block so lengthened remains the block to compare against.
+                k1 += k2
+            else:
+                # Not adjacent.  Remember the first block (k1==0 means it's
+                # the dummy we started with), and make the second block the
+                # new block to compare against.
+                if k1:
+                    non_adjacent.append((i1, j1, k1))
+                i1, j1, k1 = i2, j2, k2
+        if k1:
+            non_adjacent.append((i1, j1, k1))
+
+        non_adjacent.append( (la, lb, 0) )
+        self.matching_blocks = list(map(Match._make, non_adjacent))
+        return self.matching_blocks
+
+    def get_opcodes(self):
+        """Return list of 5-tuples describing how to turn a into b.
+
+        Each tuple is of the form (tag, i1, i2, j1, j2).  The first tuple
+        has i1 == j1 == 0, and remaining tuples have i1 == the i2 from the
+        tuple preceding it, and likewise for j1 == the previous j2.
+
+        The tags are strings, with these meanings:
+
+        'replace':  a[i1:i2] should be replaced by b[j1:j2]
+        'delete':   a[i1:i2] should be deleted.
+                    Note that j1==j2 in this case.
+        'insert':   b[j1:j2] should be inserted at a[i1:i1].
+                    Note that i1==i2 in this case.
+        'equal':    a[i1:i2] == b[j1:j2]
+
+        >>> a = "qabxcd"
+        >>> b = "abycdf"
+        >>> s = SequenceMatcher(None, a, b)
+        >>> for tag, i1, i2, j1, j2 in s.get_opcodes():
+        ...    print(("%7s a[%d:%d] (%s) b[%d:%d] (%s)" %
+        ...           (tag, i1, i2, a[i1:i2], j1, j2, b[j1:j2])))
+         delete a[0:1] (q) b[0:0] ()
+          equal a[1:3] (ab) b[0:2] (ab)
+        replace a[3:4] (x) b[2:3] (y)
+          equal a[4:6] (cd) b[3:5] (cd)
+         insert a[6:6] () b[5:6] (f)
+        """
+
+        if self.opcodes is not None:
+            return self.opcodes
+        i = j = 0
+        self.opcodes = answer = []
+        for ai, bj, size in self.get_matching_blocks():
+            # invariant:  we've pumped out correct diffs to change
+            # a[:i] into b[:j], and the next matching block is
+            # a[ai:ai+size] == b[bj:bj+size].  So we need to pump
+            # out a diff to change a[i:ai] into b[j:bj], pump out
+            # the matching block, and move (i,j) beyond the match
+            tag = ''
+            if i < ai and j < bj:
+                tag = 'replace'
+            elif i < ai:
+                tag = 'delete'
+            elif j < bj:
+                tag = 'insert'
+            if tag:
+                answer.append( (tag, i, ai, j, bj) )
+            i, j = ai+size, bj+size
+            # the list of matching blocks is terminated by a
+            # sentinel with size 0
+            if size:
+                answer.append( ('equal', ai, i, bj, j) )
+        return answer
+
+    def get_grouped_opcodes(self, n=3):
+        """ Isolate change clusters by eliminating ranges with no changes.
+
+        Return a generator of groups with up to n lines of context.
+        Each group is in the same format as returned by get_opcodes().
+
+        >>> from pprint import pprint
+        >>> a = list(map(str, range(1,40)))
+        >>> b = a[:]
+        >>> b[8:8] = ['i']     # Make an insertion
+        >>> b[20] += 'x'       # Make a replacement
+        >>> b[23:28] = []      # Make a deletion
+        >>> b[30] += 'y'       # Make another replacement
+        >>> pprint(list(SequenceMatcher(None,a,b).get_grouped_opcodes()))
+        [[('equal', 5, 8, 5, 8), ('insert', 8, 8, 8, 9), ('equal', 8, 11, 9, 12)],
+         [('equal', 16, 19, 17, 20),
+          ('replace', 19, 20, 20, 21),
+          ('equal', 20, 22, 21, 23),
+          ('delete', 22, 27, 23, 23),
+          ('equal', 27, 30, 23, 26)],
+         [('equal', 31, 34, 27, 30),
+          ('replace', 34, 35, 30, 31),
+          ('equal', 35, 38, 31, 34)]]
+        """
+
+        codes = self.get_opcodes()
+        if not codes:
+            codes = [("equal", 0, 1, 0, 1)]
+        # Fixup leading and trailing groups if they show no changes.
+        if codes[0][0] == 'equal':
+            tag, i1, i2, j1, j2 = codes[0]
+            codes[0] = tag, max(i1, i2-n), i2, max(j1, j2-n), j2
+        if codes[-1][0] == 'equal':
+            tag, i1, i2, j1, j2 = codes[-1]
+            codes[-1] = tag, i1, min(i2, i1+n), j1, min(j2, j1+n)
+
+        nn = n + n
+        group = []
+        for tag, i1, i2, j1, j2 in codes:
+            # End the current group and start a new one whenever
+            # there is a large range with no changes.
+            if tag == 'equal' and i2-i1 > nn:
+                group.append((tag, i1, min(i2, i1+n), j1, min(j2, j1+n)))
+                yield group
+                group = []
+                i1, j1 = max(i1, i2-n), max(j1, j2-n)
+            group.append((tag, i1, i2, j1 ,j2))
+        if group and not (len(group)==1 and group[0][0] == 'equal'):
+            yield group
+
+    def ratio(self):
+        """Return a measure of the sequences' similarity (float in [0,1]).
+
+        Where T is the total number of elements in both sequences, and
+        M is the number of matches, this is 2.0*M / T.
+        Note that this is 1 if the sequences are identical, and 0 if
+        they have nothing in common.
+
+        .ratio() is expensive to compute if you haven't already computed
+        .get_matching_blocks() or .get_opcodes(), in which case you may
+        want to try .quick_ratio() or .real_quick_ratio() first to get an
+        upper bound.
+
+        >>> s = SequenceMatcher(None, "abcd", "bcde")
+        >>> s.ratio()
+        0.75
+        >>> s.quick_ratio()
+        0.75
+        >>> s.real_quick_ratio()
+        1.0
+        """
+
+        matches = sum(triple[-1] for triple in self.get_matching_blocks())
+        return _calculate_ratio(matches, len(self.a) + len(self.b))
+
+    def quick_ratio(self):
+        """Return an upper bound on ratio() relatively quickly.
+
+        This isn't defined beyond that it is an upper bound on .ratio(), and
+        is faster to compute.
+        """
+
+        # viewing a and b as multisets, set matches to the cardinality
+        # of their intersection; this counts the number of matches
+        # without regard to order, so is clearly an upper bound
+        if self.fullbcount is None:
+            self.fullbcount = fullbcount = {}
+            for elt in self.b:
+                fullbcount[elt] = fullbcount.get(elt, 0) + 1
+        fullbcount = self.fullbcount
+        # avail[x] is the number of times x appears in 'b' less the
+        # number of times we've seen it in 'a' so far ... kinda
+        avail = {}
+        availhas, matches = avail.__contains__, 0
+        for elt in self.a:
+            if availhas(elt):
+                numb = avail[elt]
+            else:
+                numb = fullbcount.get(elt, 0)
+            avail[elt] = numb - 1
+            if numb > 0:
+                matches = matches + 1
+        return _calculate_ratio(matches, len(self.a) + len(self.b))
+
+    def real_quick_ratio(self):
+        """Return an upper bound on ratio() very quickly.
+
+        This isn't defined beyond that it is an upper bound on .ratio(), and
+        is faster to compute than either .ratio() or .quick_ratio().
+        """
+
+        la, lb = len(self.a), len(self.b)
+        # can't have more matches than the number of elements in the
+        # shorter sequence
+        return _calculate_ratio(min(la, lb), la + lb)
+
     __class_getitem__ = classmethod(GenericAlias)
 
 
-def get_close_matches(word, possibilities, n=3, cutoff=0.6): 
-    """Use SequenceMatcher to return list of the best "good enough" matches. 
- 
-    word is a sequence for which close matches are desired (typically a 
-    string). 
- 
-    possibilities is a list of sequences against which to match word 
-    (typically a list of strings). 
- 
-    Optional arg n (default 3) is the maximum number of close matches to 
-    return.  n must be > 0. 
- 
-    Optional arg cutoff (default 0.6) is a float in [0, 1].  Possibilities 
-    that don't score at least that similar to word are ignored. 
- 
-    The best (no more than n) matches among the possibilities are returned 
-    in a list, sorted by similarity score, most similar first. 
- 
-    >>> get_close_matches("appel", ["ape", "apple", "peach", "puppy"]) 
-    ['apple', 'ape'] 
-    >>> import keyword as _keyword 
-    >>> get_close_matches("wheel", _keyword.kwlist) 
-    ['while'] 
-    >>> get_close_matches("Apple", _keyword.kwlist) 
-    [] 
-    >>> get_close_matches("accept", _keyword.kwlist) 
-    ['except'] 
-    """ 
- 
-    if not n >  0: 
-        raise ValueError("n must be > 0: %r" % (n,)) 
-    if not 0.0 <= cutoff <= 1.0: 
-        raise ValueError("cutoff must be in [0.0, 1.0]: %r" % (cutoff,)) 
-    result = [] 
-    s = SequenceMatcher() 
-    s.set_seq2(word) 
-    for x in possibilities: 
-        s.set_seq1(x) 
-        if s.real_quick_ratio() >= cutoff and \ 
-           s.quick_ratio() >= cutoff and \ 
-           s.ratio() >= cutoff: 
-            result.append((s.ratio(), x)) 
- 
-    # Move the best scorers to head of list 
-    result = _nlargest(n, result) 
-    # Strip scores for the best n matches 
-    return [x for score, x in result] 
- 
- 
+def get_close_matches(word, possibilities, n=3, cutoff=0.6):
+    """Use SequenceMatcher to return list of the best "good enough" matches.
+
+    word is a sequence for which close matches are desired (typically a
+    string).
+
+    possibilities is a list of sequences against which to match word
+    (typically a list of strings).
+
+    Optional arg n (default 3) is the maximum number of close matches to
+    return.  n must be > 0.
+
+    Optional arg cutoff (default 0.6) is a float in [0, 1].  Possibilities
+    that don't score at least that similar to word are ignored.
+
+    The best (no more than n) matches among the possibilities are returned
+    in a list, sorted by similarity score, most similar first.
+
+    >>> get_close_matches("appel", ["ape", "apple", "peach", "puppy"])
+    ['apple', 'ape']
+    >>> import keyword as _keyword
+    >>> get_close_matches("wheel", _keyword.kwlist)
+    ['while']
+    >>> get_close_matches("Apple", _keyword.kwlist)
+    []
+    >>> get_close_matches("accept", _keyword.kwlist)
+    ['except']
+    """
+
+    if not n >  0:
+        raise ValueError("n must be > 0: %r" % (n,))
+    if not 0.0 <= cutoff <= 1.0:
+        raise ValueError("cutoff must be in [0.0, 1.0]: %r" % (cutoff,))
+    result = []
+    s = SequenceMatcher()
+    s.set_seq2(word)
+    for x in possibilities:
+        s.set_seq1(x)
+        if s.real_quick_ratio() >= cutoff and \
+           s.quick_ratio() >= cutoff and \
+           s.ratio() >= cutoff:
+            result.append((s.ratio(), x))
+
+    # Move the best scorers to head of list
+    result = _nlargest(n, result)
+    # Strip scores for the best n matches
+    return [x for score, x in result]
+
+
 def _keep_original_ws(s, tag_s):
     """Replace whitespace with the original whitespace characters in `s`"""
     return ''.join(
         c if tag_c == " " and c.isspace() else tag_c
         for c, tag_c in zip(s, tag_s)
     )
- 
- 
- 
-class Differ: 
-    r""" 
-    Differ is a class for comparing sequences of lines of text, and 
-    producing human-readable differences or deltas.  Differ uses 
-    SequenceMatcher both to compare sequences of lines, and to compare 
-    sequences of characters within similar (near-matching) lines. 
- 
-    Each line of a Differ delta begins with a two-letter code: 
- 
-        '- '    line unique to sequence 1 
-        '+ '    line unique to sequence 2 
-        '  '    line common to both sequences 
-        '? '    line not present in either input sequence 
- 
-    Lines beginning with '? ' attempt to guide the eye to intraline 
-    differences, and were not present in either input sequence.  These lines 
-    can be confusing if the sequences contain tab characters. 
- 
-    Note that Differ makes no claim to produce a *minimal* diff.  To the 
-    contrary, minimal diffs are often counter-intuitive, because they synch 
-    up anywhere possible, sometimes accidental matches 100 pages apart. 
-    Restricting synch points to contiguous matches preserves some notion of 
-    locality, at the occasional cost of producing a longer diff. 
- 
-    Example: Comparing two texts. 
- 
-    First we set up the texts, sequences of individual single-line strings 
-    ending with newlines (such sequences can also be obtained from the 
-    `readlines()` method of file-like objects): 
- 
-    >>> text1 = '''  1. Beautiful is better than ugly. 
-    ...   2. Explicit is better than implicit. 
-    ...   3. Simple is better than complex. 
-    ...   4. Complex is better than complicated. 
-    ... '''.splitlines(keepends=True) 
-    >>> len(text1) 
-    4 
-    >>> text1[0][-1] 
-    '\n' 
-    >>> text2 = '''  1. Beautiful is better than ugly. 
-    ...   3.   Simple is better than complex. 
-    ...   4. Complicated is better than complex. 
-    ...   5. Flat is better than nested. 
-    ... '''.splitlines(keepends=True) 
- 
-    Next we instantiate a Differ object: 
- 
-    >>> d = Differ() 
- 
-    Note that when instantiating a Differ object we may pass functions to 
-    filter out line and character 'junk'.  See Differ.__init__ for details. 
- 
-    Finally, we compare the two: 
- 
-    >>> result = list(d.compare(text1, text2)) 
- 
-    'result' is a list of strings, so let's pretty-print it: 
- 
-    >>> from pprint import pprint as _pprint 
-    >>> _pprint(result) 
-    ['    1. Beautiful is better than ugly.\n', 
-     '-   2. Explicit is better than implicit.\n', 
-     '-   3. Simple is better than complex.\n', 
-     '+   3.   Simple is better than complex.\n', 
-     '?     ++\n', 
-     '-   4. Complex is better than complicated.\n', 
-     '?            ^                     ---- ^\n', 
-     '+   4. Complicated is better than complex.\n', 
-     '?           ++++ ^                      ^\n', 
-     '+   5. Flat is better than nested.\n'] 
- 
-    As a single multi-line string it looks like this: 
- 
-    >>> print(''.join(result), end="") 
-        1. Beautiful is better than ugly. 
-    -   2. Explicit is better than implicit. 
-    -   3. Simple is better than complex. 
-    +   3.   Simple is better than complex. 
-    ?     ++ 
-    -   4. Complex is better than complicated. 
-    ?            ^                     ---- ^ 
-    +   4. Complicated is better than complex. 
-    ?           ++++ ^                      ^ 
-    +   5. Flat is better than nested. 
-    """ 
- 
-    def __init__(self, linejunk=None, charjunk=None): 
-        """ 
-        Construct a text differencer, with optional filters. 
- 
-        The two optional keyword parameters are for filter functions: 
- 
-        - `linejunk`: A function that should accept a single string argument, 
-          and return true iff the string is junk. The module-level function 
-          `IS_LINE_JUNK` may be used to filter out lines without visible 
-          characters, except for at most one splat ('#').  It is recommended 
-          to leave linejunk None; the underlying SequenceMatcher class has 
-          an adaptive notion of "noise" lines that's better than any static 
-          definition the author has ever been able to craft. 
- 
-        - `charjunk`: A function that should accept a string of length 1. The 
-          module-level function `IS_CHARACTER_JUNK` may be used to filter out 
-          whitespace characters (a blank or tab; **note**: bad idea to include 
-          newline in this!).  Use of IS_CHARACTER_JUNK is recommended. 
-        """ 
- 
-        self.linejunk = linejunk 
-        self.charjunk = charjunk 
- 
-    def compare(self, a, b): 
-        r""" 
-        Compare two sequences of lines; generate the resulting delta. 
- 
-        Each sequence must contain individual single-line strings ending with 
-        newlines. Such sequences can be obtained from the `readlines()` method 
-        of file-like objects.  The delta generated also consists of newline- 
-        terminated strings, ready to be printed as-is via the writeline() 
-        method of a file-like object. 
- 
-        Example: 
- 
-        >>> print(''.join(Differ().compare('one\ntwo\nthree\n'.splitlines(True), 
-        ...                                'ore\ntree\nemu\n'.splitlines(True))), 
-        ...       end="") 
-        - one 
-        ?  ^ 
-        + ore 
-        ?  ^ 
-        - two 
-        - three 
-        ?  - 
-        + tree 
-        + emu 
-        """ 
- 
-        cruncher = SequenceMatcher(self.linejunk, a, b) 
-        for tag, alo, ahi, blo, bhi in cruncher.get_opcodes(): 
-            if tag == 'replace': 
-                g = self._fancy_replace(a, alo, ahi, b, blo, bhi) 
-            elif tag == 'delete': 
-                g = self._dump('-', a, alo, ahi) 
-            elif tag == 'insert': 
-                g = self._dump('+', b, blo, bhi) 
-            elif tag == 'equal': 
-                g = self._dump(' ', a, alo, ahi) 
-            else: 
-                raise ValueError('unknown tag %r' % (tag,)) 
- 
-            yield from g 
- 
-    def _dump(self, tag, x, lo, hi): 
-        """Generate comparison results for a same-tagged range.""" 
-        for i in range(lo, hi): 
-            yield '%s %s' % (tag, x[i]) 
- 
-    def _plain_replace(self, a, alo, ahi, b, blo, bhi): 
-        assert alo < ahi and blo < bhi 
-        # dump the shorter block first -- reduces the burden on short-term 
-        # memory if the blocks are of very different sizes 
-        if bhi - blo < ahi - alo: 
-            first  = self._dump('+', b, blo, bhi) 
-            second = self._dump('-', a, alo, ahi) 
-        else: 
-            first  = self._dump('-', a, alo, ahi) 
-            second = self._dump('+', b, blo, bhi) 
- 
-        for g in first, second: 
-            yield from g 
- 
-    def _fancy_replace(self, a, alo, ahi, b, blo, bhi): 
-        r""" 
-        When replacing one block of lines with another, search the blocks 
-        for *similar* lines; the best-matching pair (if any) is used as a 
-        synch point, and intraline difference marking is done on the 
-        similar pair. Lots of work, but often worth it. 
- 
-        Example: 
- 
-        >>> d = Differ() 
-        >>> results = d._fancy_replace(['abcDefghiJkl\n'], 0, 1, 
-        ...                            ['abcdefGhijkl\n'], 0, 1) 
-        >>> print(''.join(results), end="") 
-        - abcDefghiJkl 
-        ?    ^  ^  ^ 
-        + abcdefGhijkl 
-        ?    ^  ^  ^ 
-        """ 
- 
-        # don't synch up unless the lines have a similarity score of at 
-        # least cutoff; best_ratio tracks the best score seen so far 
-        best_ratio, cutoff = 0.74, 0.75 
-        cruncher = SequenceMatcher(self.charjunk) 
-        eqi, eqj = None, None   # 1st indices of equal lines (if any) 
- 
-        # search for the pair that matches best without being identical 
-        # (identical lines must be junk lines, & we don't want to synch up 
-        # on junk -- unless we have to) 
-        for j in range(blo, bhi): 
-            bj = b[j] 
-            cruncher.set_seq2(bj) 
-            for i in range(alo, ahi): 
-                ai = a[i] 
-                if ai == bj: 
-                    if eqi is None: 
-                        eqi, eqj = i, j 
-                    continue 
-                cruncher.set_seq1(ai) 
-                # computing similarity is expensive, so use the quick 
-                # upper bounds first -- have seen this speed up messy 
-                # compares by a factor of 3. 
-                # note that ratio() is only expensive to compute the first 
-                # time it's called on a sequence pair; the expensive part 
-                # of the computation is cached by cruncher 
-                if cruncher.real_quick_ratio() > best_ratio and \ 
-                      cruncher.quick_ratio() > best_ratio and \ 
-                      cruncher.ratio() > best_ratio: 
-                    best_ratio, best_i, best_j = cruncher.ratio(), i, j 
-        if best_ratio < cutoff: 
-            # no non-identical "pretty close" pair 
-            if eqi is None: 
-                # no identical pair either -- treat it as a straight replace 
-                yield from self._plain_replace(a, alo, ahi, b, blo, bhi) 
-                return 
-            # no close pair, but an identical pair -- synch up on that 
-            best_i, best_j, best_ratio = eqi, eqj, 1.0 
-        else: 
-            # there's a close pair, so forget the identical pair (if any) 
-            eqi = None 
- 
-        # a[best_i] very similar to b[best_j]; eqi is None iff they're not 
-        # identical 
- 
-        # pump out diffs from before the synch point 
-        yield from self._fancy_helper(a, alo, best_i, b, blo, best_j) 
- 
-        # do intraline marking on the synch pair 
-        aelt, belt = a[best_i], b[best_j] 
-        if eqi is None: 
-            # pump out a '-', '?', '+', '?' quad for the synched lines 
-            atags = btags = "" 
-            cruncher.set_seqs(aelt, belt) 
-            for tag, ai1, ai2, bj1, bj2 in cruncher.get_opcodes(): 
-                la, lb = ai2 - ai1, bj2 - bj1 
-                if tag == 'replace': 
-                    atags += '^' * la 
-                    btags += '^' * lb 
-                elif tag == 'delete': 
-                    atags += '-' * la 
-                elif tag == 'insert': 
-                    btags += '+' * lb 
-                elif tag == 'equal': 
-                    atags += ' ' * la 
-                    btags += ' ' * lb 
-                else: 
-                    raise ValueError('unknown tag %r' % (tag,)) 
-            yield from self._qformat(aelt, belt, atags, btags) 
-        else: 
-            # the synch pair is identical 
-            yield '  ' + aelt 
- 
-        # pump out diffs from after the synch point 
-        yield from self._fancy_helper(a, best_i+1, ahi, b, best_j+1, bhi) 
- 
-    def _fancy_helper(self, a, alo, ahi, b, blo, bhi): 
-        g = [] 
-        if alo < ahi: 
-            if blo < bhi: 
-                g = self._fancy_replace(a, alo, ahi, b, blo, bhi) 
-            else: 
-                g = self._dump('-', a, alo, ahi) 
-        elif blo < bhi: 
-            g = self._dump('+', b, blo, bhi) 
- 
-        yield from g 
- 
-    def _qformat(self, aline, bline, atags, btags): 
-        r""" 
+
+
+
+class Differ:
+    r"""
+    Differ is a class for comparing sequences of lines of text, and
+    producing human-readable differences or deltas.  Differ uses
+    SequenceMatcher both to compare sequences of lines, and to compare
+    sequences of characters within similar (near-matching) lines.
+
+    Each line of a Differ delta begins with a two-letter code:
+
+        '- '    line unique to sequence 1
+        '+ '    line unique to sequence 2
+        '  '    line common to both sequences
+        '? '    line not present in either input sequence
+
+    Lines beginning with '? ' attempt to guide the eye to intraline
+    differences, and were not present in either input sequence.  These lines
+    can be confusing if the sequences contain tab characters.
+
+    Note that Differ makes no claim to produce a *minimal* diff.  To the
+    contrary, minimal diffs are often counter-intuitive, because they synch
+    up anywhere possible, sometimes accidental matches 100 pages apart.
+    Restricting synch points to contiguous matches preserves some notion of
+    locality, at the occasional cost of producing a longer diff.
+
+    Example: Comparing two texts.
+
+    First we set up the texts, sequences of individual single-line strings
+    ending with newlines (such sequences can also be obtained from the
+    `readlines()` method of file-like objects):
+
+    >>> text1 = '''  1. Beautiful is better than ugly.
+    ...   2. Explicit is better than implicit.
+    ...   3. Simple is better than complex.
+    ...   4. Complex is better than complicated.
+    ... '''.splitlines(keepends=True)
+    >>> len(text1)
+    4
+    >>> text1[0][-1]
+    '\n'
+    >>> text2 = '''  1. Beautiful is better than ugly.
+    ...   3.   Simple is better than complex.
+    ...   4. Complicated is better than complex.
+    ...   5. Flat is better than nested.
+    ... '''.splitlines(keepends=True)
+
+    Next we instantiate a Differ object:
+
+    >>> d = Differ()
+
+    Note that when instantiating a Differ object we may pass functions to
+    filter out line and character 'junk'.  See Differ.__init__ for details.
+
+    Finally, we compare the two:
+
+    >>> result = list(d.compare(text1, text2))
+
+    'result' is a list of strings, so let's pretty-print it:
+
+    >>> from pprint import pprint as _pprint
+    >>> _pprint(result)
+    ['    1. Beautiful is better than ugly.\n',
+     '-   2. Explicit is better than implicit.\n',
+     '-   3. Simple is better than complex.\n',
+     '+   3.   Simple is better than complex.\n',
+     '?     ++\n',
+     '-   4. Complex is better than complicated.\n',
+     '?            ^                     ---- ^\n',
+     '+   4. Complicated is better than complex.\n',
+     '?           ++++ ^                      ^\n',
+     '+   5. Flat is better than nested.\n']
+
+    As a single multi-line string it looks like this:
+
+    >>> print(''.join(result), end="")
+        1. Beautiful is better than ugly.
+    -   2. Explicit is better than implicit.
+    -   3. Simple is better than complex.
+    +   3.   Simple is better than complex.
+    ?     ++
+    -   4. Complex is better than complicated.
+    ?            ^                     ---- ^
+    +   4. Complicated is better than complex.
+    ?           ++++ ^                      ^
+    +   5. Flat is better than nested.
+    """
+
+    def __init__(self, linejunk=None, charjunk=None):
+        """
+        Construct a text differencer, with optional filters.
+
+        The two optional keyword parameters are for filter functions:
+
+        - `linejunk`: A function that should accept a single string argument,
+          and return true iff the string is junk. The module-level function
+          `IS_LINE_JUNK` may be used to filter out lines without visible
+          characters, except for at most one splat ('#').  It is recommended
+          to leave linejunk None; the underlying SequenceMatcher class has
+          an adaptive notion of "noise" lines that's better than any static
+          definition the author has ever been able to craft.
+
+        - `charjunk`: A function that should accept a string of length 1. The
+          module-level function `IS_CHARACTER_JUNK` may be used to filter out
+          whitespace characters (a blank or tab; **note**: bad idea to include
+          newline in this!).  Use of IS_CHARACTER_JUNK is recommended.
+        """
+
+        self.linejunk = linejunk
+        self.charjunk = charjunk
+
+    def compare(self, a, b):
+        r"""
+        Compare two sequences of lines; generate the resulting delta.
+
+        Each sequence must contain individual single-line strings ending with
+        newlines. Such sequences can be obtained from the `readlines()` method
+        of file-like objects.  The delta generated also consists of newline-
+        terminated strings, ready to be printed as-is via the writeline()
+        method of a file-like object.
+
+        Example:
+
+        >>> print(''.join(Differ().compare('one\ntwo\nthree\n'.splitlines(True),
+        ...                                'ore\ntree\nemu\n'.splitlines(True))),
+        ...       end="")
+        - one
+        ?  ^
+        + ore
+        ?  ^
+        - two
+        - three
+        ?  -
+        + tree
+        + emu
+        """
+
+        cruncher = SequenceMatcher(self.linejunk, a, b)
+        for tag, alo, ahi, blo, bhi in cruncher.get_opcodes():
+            if tag == 'replace':
+                g = self._fancy_replace(a, alo, ahi, b, blo, bhi)
+            elif tag == 'delete':
+                g = self._dump('-', a, alo, ahi)
+            elif tag == 'insert':
+                g = self._dump('+', b, blo, bhi)
+            elif tag == 'equal':
+                g = self._dump(' ', a, alo, ahi)
+            else:
+                raise ValueError('unknown tag %r' % (tag,))
+
+            yield from g
+
+    def _dump(self, tag, x, lo, hi):
+        """Generate comparison results for a same-tagged range."""
+        for i in range(lo, hi):
+            yield '%s %s' % (tag, x[i])
+
+    def _plain_replace(self, a, alo, ahi, b, blo, bhi):
+        assert alo < ahi and blo < bhi
+        # dump the shorter block first -- reduces the burden on short-term
+        # memory if the blocks are of very different sizes
+        if bhi - blo < ahi - alo:
+            first  = self._dump('+', b, blo, bhi)
+            second = self._dump('-', a, alo, ahi)
+        else:
+            first  = self._dump('-', a, alo, ahi)
+            second = self._dump('+', b, blo, bhi)
+
+        for g in first, second:
+            yield from g
+
+    def _fancy_replace(self, a, alo, ahi, b, blo, bhi):
+        r"""
+        When replacing one block of lines with another, search the blocks
+        for *similar* lines; the best-matching pair (if any) is used as a
+        synch point, and intraline difference marking is done on the
+        similar pair. Lots of work, but often worth it.
+
+        Example:
+
+        >>> d = Differ()
+        >>> results = d._fancy_replace(['abcDefghiJkl\n'], 0, 1,
+        ...                            ['abcdefGhijkl\n'], 0, 1)
+        >>> print(''.join(results), end="")
+        - abcDefghiJkl
+        ?    ^  ^  ^
+        + abcdefGhijkl
+        ?    ^  ^  ^
+        """
+
+        # don't synch up unless the lines have a similarity score of at
+        # least cutoff; best_ratio tracks the best score seen so far
+        best_ratio, cutoff = 0.74, 0.75
+        cruncher = SequenceMatcher(self.charjunk)
+        eqi, eqj = None, None   # 1st indices of equal lines (if any)
+
+        # search for the pair that matches best without being identical
+        # (identical lines must be junk lines, & we don't want to synch up
+        # on junk -- unless we have to)
+        for j in range(blo, bhi):
+            bj = b[j]
+            cruncher.set_seq2(bj)
+            for i in range(alo, ahi):
+                ai = a[i]
+                if ai == bj:
+                    if eqi is None:
+                        eqi, eqj = i, j
+                    continue
+                cruncher.set_seq1(ai)
+                # computing similarity is expensive, so use the quick
+                # upper bounds first -- have seen this speed up messy
+                # compares by a factor of 3.
+                # note that ratio() is only expensive to compute the first
+                # time it's called on a sequence pair; the expensive part
+                # of the computation is cached by cruncher
+                if cruncher.real_quick_ratio() > best_ratio and \
+                      cruncher.quick_ratio() > best_ratio and \
+                      cruncher.ratio() > best_ratio:
+                    best_ratio, best_i, best_j = cruncher.ratio(), i, j
+        if best_ratio < cutoff:
+            # no non-identical "pretty close" pair
+            if eqi is None:
+                # no identical pair either -- treat it as a straight replace
+                yield from self._plain_replace(a, alo, ahi, b, blo, bhi)
+                return
+            # no close pair, but an identical pair -- synch up on that
+            best_i, best_j, best_ratio = eqi, eqj, 1.0
+        else:
+            # there's a close pair, so forget the identical pair (if any)
+            eqi = None
+
+        # a[best_i] very similar to b[best_j]; eqi is None iff they're not
+        # identical
+
+        # pump out diffs from before the synch point
+        yield from self._fancy_helper(a, alo, best_i, b, blo, best_j)
+
+        # do intraline marking on the synch pair
+        aelt, belt = a[best_i], b[best_j]
+        if eqi is None:
+            # pump out a '-', '?', '+', '?' quad for the synched lines
+            atags = btags = ""
+            cruncher.set_seqs(aelt, belt)
+            for tag, ai1, ai2, bj1, bj2 in cruncher.get_opcodes():
+                la, lb = ai2 - ai1, bj2 - bj1
+                if tag == 'replace':
+                    atags += '^' * la
+                    btags += '^' * lb
+                elif tag == 'delete':
+                    atags += '-' * la
+                elif tag == 'insert':
+                    btags += '+' * lb
+                elif tag == 'equal':
+                    atags += ' ' * la
+                    btags += ' ' * lb
+                else:
+                    raise ValueError('unknown tag %r' % (tag,))
+            yield from self._qformat(aelt, belt, atags, btags)
+        else:
+            # the synch pair is identical
+            yield '  ' + aelt
+
+        # pump out diffs from after the synch point
+        yield from self._fancy_helper(a, best_i+1, ahi, b, best_j+1, bhi)
+
+    def _fancy_helper(self, a, alo, ahi, b, blo, bhi):
+        g = []
+        if alo < ahi:
+            if blo < bhi:
+                g = self._fancy_replace(a, alo, ahi, b, blo, bhi)
+            else:
+                g = self._dump('-', a, alo, ahi)
+        elif blo < bhi:
+            g = self._dump('+', b, blo, bhi)
+
+        yield from g
+
+    def _qformat(self, aline, bline, atags, btags):
+        r"""
         Format "?" output and deal with tabs.
- 
-        Example: 
- 
-        >>> d = Differ() 
-        >>> results = d._qformat('\tabcDefghiJkl\n', '\tabcdefGhijkl\n', 
-        ...                      '  ^ ^  ^      ', '  ^ ^  ^      ') 
-        >>> for line in results: print(repr(line)) 
-        ... 
-        '- \tabcDefghiJkl\n' 
-        '? \t ^ ^  ^\n' 
-        '+ \tabcdefGhijkl\n' 
-        '? \t ^ ^  ^\n' 
-        """ 
+
+        Example:
+
+        >>> d = Differ()
+        >>> results = d._qformat('\tabcDefghiJkl\n', '\tabcdefGhijkl\n',
+        ...                      '  ^ ^  ^      ', '  ^ ^  ^      ')
+        >>> for line in results: print(repr(line))
+        ...
+        '- \tabcDefghiJkl\n'
+        '? \t ^ ^  ^\n'
+        '+ \tabcdefGhijkl\n'
+        '? \t ^ ^  ^\n'
+        """
         atags = _keep_original_ws(aline, atags).rstrip()
         btags = _keep_original_ws(bline, btags).rstrip()
- 
-        yield "- " + aline 
-        if atags: 
+
+        yield "- " + aline
+        if atags:
             yield f"? {atags}\n"
- 
-        yield "+ " + bline 
-        if btags: 
+
+        yield "+ " + bline
+        if btags:
             yield f"? {btags}\n"
- 
-# With respect to junk, an earlier version of ndiff simply refused to 
-# *start* a match with a junk element.  The result was cases like this: 
-#     before: private Thread currentThread; 
-#     after:  private volatile Thread currentThread; 
-# If you consider whitespace to be junk, the longest contiguous match 
-# not starting with junk is "e Thread currentThread".  So ndiff reported 
-# that "e volatil" was inserted between the 't' and the 'e' in "private". 
-# While an accurate view, to people that's absurd.  The current version 
-# looks for matching blocks that are entirely junk-free, then extends the 
-# longest one of those as far as possible but only with matching junk. 
-# So now "currentThread" is matched, then extended to suck up the 
-# preceding blank; then "private" is matched, and extended to suck up the 
-# following blank; then "Thread" is matched; and finally ndiff reports 
-# that "volatile " was inserted before "Thread".  The only quibble 
-# remaining is that perhaps it was really the case that " volatile" 
-# was inserted after "private".  I can live with that <wink>. 
- 
-import re 
- 
-def IS_LINE_JUNK(line, pat=re.compile(r"\s*(?:#\s*)?$").match): 
-    r""" 
+
+# With respect to junk, an earlier version of ndiff simply refused to
+# *start* a match with a junk element.  The result was cases like this:
+#     before: private Thread currentThread;
+#     after:  private volatile Thread currentThread;
+# If you consider whitespace to be junk, the longest contiguous match
+# not starting with junk is "e Thread currentThread".  So ndiff reported
+# that "e volatil" was inserted between the 't' and the 'e' in "private".
+# While an accurate view, to people that's absurd.  The current version
+# looks for matching blocks that are entirely junk-free, then extends the
+# longest one of those as far as possible but only with matching junk.
+# So now "currentThread" is matched, then extended to suck up the
+# preceding blank; then "private" is matched, and extended to suck up the
+# following blank; then "Thread" is matched; and finally ndiff reports
+# that "volatile " was inserted before "Thread".  The only quibble
+# remaining is that perhaps it was really the case that " volatile"
+# was inserted after "private".  I can live with that <wink>.
+
+import re
+
+def IS_LINE_JUNK(line, pat=re.compile(r"\s*(?:#\s*)?$").match):
+    r"""
     Return True for ignorable line: iff `line` is blank or contains a single '#'.
- 
-    Examples: 
- 
-    >>> IS_LINE_JUNK('\n') 
-    True 
-    >>> IS_LINE_JUNK('  #   \n') 
-    True 
-    >>> IS_LINE_JUNK('hello\n') 
-    False 
-    """ 
- 
-    return pat(line) is not None 
- 
-def IS_CHARACTER_JUNK(ch, ws=" \t"): 
-    r""" 
+
+    Examples:
+
+    >>> IS_LINE_JUNK('\n')
+    True
+    >>> IS_LINE_JUNK('  #   \n')
+    True
+    >>> IS_LINE_JUNK('hello\n')
+    False
+    """
+
+    return pat(line) is not None
+
+def IS_CHARACTER_JUNK(ch, ws=" \t"):
+    r"""
     Return True for ignorable character: iff `ch` is a space or tab.
- 
-    Examples: 
- 
-    >>> IS_CHARACTER_JUNK(' ') 
-    True 
-    >>> IS_CHARACTER_JUNK('\t') 
-    True 
-    >>> IS_CHARACTER_JUNK('\n') 
-    False 
-    >>> IS_CHARACTER_JUNK('x') 
-    False 
-    """ 
- 
-    return ch in ws 
- 
- 
-######################################################################## 
-###  Unified Diff 
-######################################################################## 
- 
-def _format_range_unified(start, stop): 
-    'Convert range to the "ed" format' 
-    # Per the diff spec at http://www.unix.org/single_unix_specification/ 
-    beginning = start + 1     # lines start numbering with one 
-    length = stop - start 
-    if length == 1: 
-        return '{}'.format(beginning) 
-    if not length: 
-        beginning -= 1        # empty ranges begin at line just before the range 
-    return '{},{}'.format(beginning, length) 
- 
-def unified_diff(a, b, fromfile='', tofile='', fromfiledate='', 
-                 tofiledate='', n=3, lineterm='\n'): 
-    r""" 
-    Compare two sequences of lines; generate the delta as a unified diff. 
- 
-    Unified diffs are a compact way of showing line changes and a few 
-    lines of context.  The number of context lines is set by 'n' which 
-    defaults to three. 
- 
-    By default, the diff control lines (those with ---, +++, or @@) are 
-    created with a trailing newline.  This is helpful so that inputs 
-    created from file.readlines() result in diffs that are suitable for 
-    file.writelines() since both the inputs and outputs have trailing 
-    newlines. 
- 
-    For inputs that do not have trailing newlines, set the lineterm 
-    argument to "" so that the output will be uniformly newline free. 
- 
-    The unidiff format normally has a header for filenames and modification 
-    times.  Any or all of these may be specified using strings for 
-    'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'. 
-    The modification times are normally expressed in the ISO 8601 format. 
- 
-    Example: 
- 
-    >>> for line in unified_diff('one two three four'.split(), 
-    ...             'zero one tree four'.split(), 'Original', 'Current', 
-    ...             '2005-01-26 23:30:50', '2010-04-02 10:20:52', 
-    ...             lineterm=''): 
-    ...     print(line)                 # doctest: +NORMALIZE_WHITESPACE 
-    --- Original        2005-01-26 23:30:50 
-    +++ Current         2010-04-02 10:20:52 
-    @@ -1,4 +1,4 @@ 
-    +zero 
-     one 
-    -two 
-    -three 
-    +tree 
-     four 
-    """ 
- 
-    _check_types(a, b, fromfile, tofile, fromfiledate, tofiledate, lineterm) 
-    started = False 
-    for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n): 
-        if not started: 
-            started = True 
-            fromdate = '\t{}'.format(fromfiledate) if fromfiledate else '' 
-            todate = '\t{}'.format(tofiledate) if tofiledate else '' 
-            yield '--- {}{}{}'.format(fromfile, fromdate, lineterm) 
-            yield '+++ {}{}{}'.format(tofile, todate, lineterm) 
- 
-        first, last = group[0], group[-1] 
-        file1_range = _format_range_unified(first[1], last[2]) 
-        file2_range = _format_range_unified(first[3], last[4]) 
-        yield '@@ -{} +{} @@{}'.format(file1_range, file2_range, lineterm) 
- 
-        for tag, i1, i2, j1, j2 in group: 
-            if tag == 'equal': 
-                for line in a[i1:i2]: 
-                    yield ' ' + line 
-                continue 
-            if tag in {'replace', 'delete'}: 
-                for line in a[i1:i2]: 
-                    yield '-' + line 
-            if tag in {'replace', 'insert'}: 
-                for line in b[j1:j2]: 
-                    yield '+' + line 
- 
- 
-######################################################################## 
-###  Context Diff 
-######################################################################## 
- 
-def _format_range_context(start, stop): 
-    'Convert range to the "ed" format' 
-    # Per the diff spec at http://www.unix.org/single_unix_specification/ 
-    beginning = start + 1     # lines start numbering with one 
-    length = stop - start 
-    if not length: 
-        beginning -= 1        # empty ranges begin at line just before the range 
-    if length <= 1: 
-        return '{}'.format(beginning) 
-    return '{},{}'.format(beginning, beginning + length - 1) 
- 
-# See http://www.unix.org/single_unix_specification/ 
-def context_diff(a, b, fromfile='', tofile='', 
-                 fromfiledate='', tofiledate='', n=3, lineterm='\n'): 
-    r""" 
-    Compare two sequences of lines; generate the delta as a context diff. 
- 
-    Context diffs are a compact way of showing line changes and a few 
-    lines of context.  The number of context lines is set by 'n' which 
-    defaults to three. 
- 
-    By default, the diff control lines (those with *** or ---) are 
-    created with a trailing newline.  This is helpful so that inputs 
-    created from file.readlines() result in diffs that are suitable for 
-    file.writelines() since both the inputs and outputs have trailing 
-    newlines. 
- 
-    For inputs that do not have trailing newlines, set the lineterm 
-    argument to "" so that the output will be uniformly newline free. 
- 
-    The context diff format normally has a header for filenames and 
-    modification times.  Any or all of these may be specified using 
-    strings for 'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'. 
-    The modification times are normally expressed in the ISO 8601 format. 
-    If not specified, the strings default to blanks. 
- 
-    Example: 
- 
-    >>> print(''.join(context_diff('one\ntwo\nthree\nfour\n'.splitlines(True), 
-    ...       'zero\none\ntree\nfour\n'.splitlines(True), 'Original', 'Current')), 
-    ...       end="") 
-    *** Original 
-    --- Current 
-    *************** 
-    *** 1,4 **** 
-      one 
-    ! two 
-    ! three 
-      four 
-    --- 1,4 ---- 
-    + zero 
-      one 
-    ! tree 
-      four 
-    """ 
- 
-    _check_types(a, b, fromfile, tofile, fromfiledate, tofiledate, lineterm) 
-    prefix = dict(insert='+ ', delete='- ', replace='! ', equal='  ') 
-    started = False 
-    for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n): 
-        if not started: 
-            started = True 
-            fromdate = '\t{}'.format(fromfiledate) if fromfiledate else '' 
-            todate = '\t{}'.format(tofiledate) if tofiledate else '' 
-            yield '*** {}{}{}'.format(fromfile, fromdate, lineterm) 
-            yield '--- {}{}{}'.format(tofile, todate, lineterm) 
- 
-        first, last = group[0], group[-1] 
-        yield '***************' + lineterm 
- 
-        file1_range = _format_range_context(first[1], last[2]) 
-        yield '*** {} ****{}'.format(file1_range, lineterm) 
- 
-        if any(tag in {'replace', 'delete'} for tag, _, _, _, _ in group): 
-            for tag, i1, i2, _, _ in group: 
-                if tag != 'insert': 
-                    for line in a[i1:i2]: 
-                        yield prefix[tag] + line 
- 
-        file2_range = _format_range_context(first[3], last[4]) 
-        yield '--- {} ----{}'.format(file2_range, lineterm) 
- 
-        if any(tag in {'replace', 'insert'} for tag, _, _, _, _ in group): 
-            for tag, _, _, j1, j2 in group: 
-                if tag != 'delete': 
-                    for line in b[j1:j2]: 
-                        yield prefix[tag] + line 
- 
-def _check_types(a, b, *args): 
-    # Checking types is weird, but the alternative is garbled output when 
-    # someone passes mixed bytes and str to {unified,context}_diff(). E.g. 
-    # without this check, passing filenames as bytes results in output like 
-    #   --- b'oldfile.txt' 
-    #   +++ b'newfile.txt' 
-    # because of how str.format() incorporates bytes objects. 
-    if a and not isinstance(a[0], str): 
-        raise TypeError('lines to compare must be str, not %s (%r)' % 
-                        (type(a[0]).__name__, a[0])) 
-    if b and not isinstance(b[0], str): 
-        raise TypeError('lines to compare must be str, not %s (%r)' % 
-                        (type(b[0]).__name__, b[0])) 
-    for arg in args: 
-        if not isinstance(arg, str): 
-            raise TypeError('all arguments must be str, not: %r' % (arg,)) 
- 
-def diff_bytes(dfunc, a, b, fromfile=b'', tofile=b'', 
-               fromfiledate=b'', tofiledate=b'', n=3, lineterm=b'\n'): 
-    r""" 
-    Compare `a` and `b`, two sequences of lines represented as bytes rather 
-    than str. This is a wrapper for `dfunc`, which is typically either 
-    unified_diff() or context_diff(). Inputs are losslessly converted to 
-    strings so that `dfunc` only has to worry about strings, and encoded 
-    back to bytes on return. This is necessary to compare files with 
-    unknown or inconsistent encoding. All other inputs (except `n`) must be 
-    bytes rather than str. 
-    """ 
-    def decode(s): 
-        try: 
-            return s.decode('ascii', 'surrogateescape') 
-        except AttributeError as err: 
-            msg = ('all arguments must be bytes, not %s (%r)' % 
-                   (type(s).__name__, s)) 
-            raise TypeError(msg) from err 
-    a = list(map(decode, a)) 
-    b = list(map(decode, b)) 
-    fromfile = decode(fromfile) 
-    tofile = decode(tofile) 
-    fromfiledate = decode(fromfiledate) 
-    tofiledate = decode(tofiledate) 
-    lineterm = decode(lineterm) 
- 
-    lines = dfunc(a, b, fromfile, tofile, fromfiledate, tofiledate, n, lineterm) 
-    for line in lines: 
-        yield line.encode('ascii', 'surrogateescape') 
- 
-def ndiff(a, b, linejunk=None, charjunk=IS_CHARACTER_JUNK): 
-    r""" 
-    Compare `a` and `b` (lists of strings); return a `Differ`-style delta. 
- 
-    Optional keyword parameters `linejunk` and `charjunk` are for filter 
-    functions, or can be None: 
- 
-    - linejunk: A function that should accept a single string argument and 
-      return true iff the string is junk.  The default is None, and is 
-      recommended; the underlying SequenceMatcher class has an adaptive 
-      notion of "noise" lines. 
- 
-    - charjunk: A function that accepts a character (string of length 
-      1), and returns true iff the character is junk. The default is 
-      the module-level function IS_CHARACTER_JUNK, which filters out 
-      whitespace characters (a blank or tab; note: it's a bad idea to 
-      include newline in this!). 
- 
-    Tools/scripts/ndiff.py is a command-line front-end to this function. 
- 
-    Example: 
- 
-    >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(keepends=True), 
-    ...              'ore\ntree\nemu\n'.splitlines(keepends=True)) 
-    >>> print(''.join(diff), end="") 
-    - one 
-    ?  ^ 
-    + ore 
-    ?  ^ 
-    - two 
-    - three 
-    ?  - 
-    + tree 
-    + emu 
-    """ 
-    return Differ(linejunk, charjunk).compare(a, b) 
- 
-def _mdiff(fromlines, tolines, context=None, linejunk=None, 
-           charjunk=IS_CHARACTER_JUNK): 
-    r"""Returns generator yielding marked up from/to side by side differences. 
- 
-    Arguments: 
-    fromlines -- list of text lines to compared to tolines 
-    tolines -- list of text lines to be compared to fromlines 
-    context -- number of context lines to display on each side of difference, 
-               if None, all from/to text lines will be generated. 
-    linejunk -- passed on to ndiff (see ndiff documentation) 
-    charjunk -- passed on to ndiff (see ndiff documentation) 
- 
-    This function returns an iterator which returns a tuple: 
-    (from line tuple, to line tuple, boolean flag) 
- 
-    from/to line tuple -- (line num, line text) 
-        line num -- integer or None (to indicate a context separation) 
-        line text -- original line text with following markers inserted: 
-            '\0+' -- marks start of added text 
-            '\0-' -- marks start of deleted text 
-            '\0^' -- marks start of changed text 
-            '\1' -- marks end of added/deleted/changed text 
- 
-    boolean flag -- None indicates context separation, True indicates 
-        either "from" or "to" line contains a change, otherwise False. 
- 
-    This function/iterator was originally developed to generate side by side 
-    file difference for making HTML pages (see HtmlDiff class for example 
-    usage). 
- 
-    Note, this function utilizes the ndiff function to generate the side by 
-    side difference markup.  Optional ndiff arguments may be passed to this 
-    function and they in turn will be passed to ndiff. 
-    """ 
-    import re 
- 
-    # regular expression for finding intraline change indices 
-    change_re = re.compile(r'(\++|\-+|\^+)') 
- 
-    # create the difference iterator to generate the differences 
-    diff_lines_iterator = ndiff(fromlines,tolines,linejunk,charjunk) 
- 
-    def _make_line(lines, format_key, side, num_lines=[0,0]): 
-        """Returns line of text with user's change markup and line formatting. 
- 
-        lines -- list of lines from the ndiff generator to produce a line of 
-                 text from.  When producing the line of text to return, the 
-                 lines used are removed from this list. 
-        format_key -- '+' return first line in list with "add" markup around 
-                          the entire line. 
-                      '-' return first line in list with "delete" markup around 
-                          the entire line. 
-                      '?' return first line in list with add/delete/change 
-                          intraline markup (indices obtained from second line) 
-                      None return first line in list with no markup 
-        side -- indice into the num_lines list (0=from,1=to) 
-        num_lines -- from/to current line number.  This is NOT intended to be a 
-                     passed parameter.  It is present as a keyword argument to 
-                     maintain memory of the current line numbers between calls 
-                     of this function. 
- 
-        Note, this function is purposefully not defined at the module scope so 
-        that data it needs from its parent function (within whose context it 
-        is defined) does not need to be of module scope. 
-        """ 
-        num_lines[side] += 1 
-        # Handle case where no user markup is to be added, just return line of 
-        # text with user's line format to allow for usage of the line number. 
-        if format_key is None: 
-            return (num_lines[side],lines.pop(0)[2:]) 
-        # Handle case of intraline changes 
-        if format_key == '?': 
-            text, markers = lines.pop(0), lines.pop(0) 
-            # find intraline changes (store change type and indices in tuples) 
-            sub_info = [] 
-            def record_sub_info(match_object,sub_info=sub_info): 
-                sub_info.append([match_object.group(1)[0],match_object.span()]) 
-                return match_object.group(1) 
-            change_re.sub(record_sub_info,markers) 
-            # process each tuple inserting our special marks that won't be 
-            # noticed by an xml/html escaper. 
-            for key,(begin,end) in reversed(sub_info): 
-                text = text[0:begin]+'\0'+key+text[begin:end]+'\1'+text[end:] 
-            text = text[2:] 
-        # Handle case of add/delete entire line 
-        else: 
-            text = lines.pop(0)[2:] 
-            # if line of text is just a newline, insert a space so there is 
-            # something for the user to highlight and see. 
-            if not text: 
-                text = ' ' 
-            # insert marks that won't be noticed by an xml/html escaper. 
-            text = '\0' + format_key + text + '\1' 
-        # Return line of text, first allow user's line formatter to do its 
-        # thing (such as adding the line number) then replace the special 
-        # marks with what the user's change markup. 
-        return (num_lines[side],text) 
- 
-    def _line_iterator(): 
-        """Yields from/to lines of text with a change indication. 
- 
-        This function is an iterator.  It itself pulls lines from a 
-        differencing iterator, processes them and yields them.  When it can 
-        it yields both a "from" and a "to" line, otherwise it will yield one 
-        or the other.  In addition to yielding the lines of from/to text, a 
-        boolean flag is yielded to indicate if the text line(s) have 
-        differences in them. 
- 
-        Note, this function is purposefully not defined at the module scope so 
-        that data it needs from its parent function (within whose context it 
-        is defined) does not need to be of module scope. 
-        """ 
-        lines = [] 
-        num_blanks_pending, num_blanks_to_yield = 0, 0 
-        while True: 
-            # Load up next 4 lines so we can look ahead, create strings which 
-            # are a concatenation of the first character of each of the 4 lines 
-            # so we can do some very readable comparisons. 
-            while len(lines) < 4: 
-                lines.append(next(diff_lines_iterator, 'X')) 
-            s = ''.join([line[0] for line in lines]) 
-            if s.startswith('X'): 
-                # When no more lines, pump out any remaining blank lines so the 
-                # corresponding add/delete lines get a matching blank line so 
-                # all line pairs get yielded at the next level. 
-                num_blanks_to_yield = num_blanks_pending 
-            elif s.startswith('-?+?'): 
-                # simple intraline change 
-                yield _make_line(lines,'?',0), _make_line(lines,'?',1), True 
-                continue 
-            elif s.startswith('--++'): 
-                # in delete block, add block coming: we do NOT want to get 
-                # caught up on blank lines yet, just process the delete line 
-                num_blanks_pending -= 1 
-                yield _make_line(lines,'-',0), None, True 
-                continue 
-            elif s.startswith(('--?+', '--+', '- ')): 
-                # in delete block and see an intraline change or unchanged line 
-                # coming: yield the delete line and then blanks 
-                from_line,to_line = _make_line(lines,'-',0), None 
-                num_blanks_to_yield,num_blanks_pending = num_blanks_pending-1,0 
-            elif s.startswith('-+?'): 
-                # intraline change 
-                yield _make_line(lines,None,0), _make_line(lines,'?',1), True 
-                continue 
-            elif s.startswith('-?+'): 
-                # intraline change 
-                yield _make_line(lines,'?',0), _make_line(lines,None,1), True 
-                continue 
-            elif s.startswith('-'): 
-                # delete FROM line 
-                num_blanks_pending -= 1 
-                yield _make_line(lines,'-',0), None, True 
-                continue 
-            elif s.startswith('+--'): 
-                # in add block, delete block coming: we do NOT want to get 
-                # caught up on blank lines yet, just process the add line 
-                num_blanks_pending += 1 
-                yield None, _make_line(lines,'+',1), True 
-                continue 
-            elif s.startswith(('+ ', '+-')): 
-                # will be leaving an add block: yield blanks then add line 
-                from_line, to_line = None, _make_line(lines,'+',1) 
-                num_blanks_to_yield,num_blanks_pending = num_blanks_pending+1,0 
-            elif s.startswith('+'): 
-                # inside an add block, yield the add line 
-                num_blanks_pending += 1 
-                yield None, _make_line(lines,'+',1), True 
-                continue 
-            elif s.startswith(' '): 
-                # unchanged text, yield it to both sides 
-                yield _make_line(lines[:],None,0),_make_line(lines,None,1),False 
-                continue 
-            # Catch up on the blank lines so when we yield the next from/to 
-            # pair, they are lined up. 
-            while(num_blanks_to_yield < 0): 
-                num_blanks_to_yield += 1 
-                yield None,('','\n'),True 
-            while(num_blanks_to_yield > 0): 
-                num_blanks_to_yield -= 1 
-                yield ('','\n'),None,True 
-            if s.startswith('X'): 
-                return 
-            else: 
-                yield from_line,to_line,True 
- 
-    def _line_pair_iterator(): 
-        """Yields from/to lines of text with a change indication. 
- 
-        This function is an iterator.  It itself pulls lines from the line 
-        iterator.  Its difference from that iterator is that this function 
-        always yields a pair of from/to text lines (with the change 
-        indication).  If necessary it will collect single from/to lines 
-        until it has a matching pair from/to pair to yield. 
- 
-        Note, this function is purposefully not defined at the module scope so 
-        that data it needs from its parent function (within whose context it 
-        is defined) does not need to be of module scope. 
-        """ 
-        line_iterator = _line_iterator() 
-        fromlines,tolines=[],[] 
-        while True: 
-            # Collecting lines of text until we have a from/to pair 
-            while (len(fromlines)==0 or len(tolines)==0): 
-                try: 
-                    from_line, to_line, found_diff = next(line_iterator) 
-                except StopIteration: 
-                    return 
-                if from_line is not None: 
-                    fromlines.append((from_line,found_diff)) 
-                if to_line is not None: 
-                    tolines.append((to_line,found_diff)) 
-            # Once we have a pair, remove them from the collection and yield it 
-            from_line, fromDiff = fromlines.pop(0) 
-            to_line, to_diff = tolines.pop(0) 
-            yield (from_line,to_line,fromDiff or to_diff) 
- 
-    # Handle case where user does not want context differencing, just yield 
-    # them up without doing anything else with them. 
-    line_pair_iterator = _line_pair_iterator() 
-    if context is None: 
-        yield from line_pair_iterator 
-    # Handle case where user wants context differencing.  We must do some 
-    # storage of lines until we know for sure that they are to be yielded. 
-    else: 
-        context += 1 
-        lines_to_write = 0 
-        while True: 
-            # Store lines up until we find a difference, note use of a 
-            # circular queue because we only need to keep around what 
-            # we need for context. 
-            index, contextLines = 0, [None]*(context) 
-            found_diff = False 
-            while(found_diff is False): 
-                try: 
-                    from_line, to_line, found_diff = next(line_pair_iterator) 
-                except StopIteration: 
-                    return 
-                i = index % context 
-                contextLines[i] = (from_line, to_line, found_diff) 
-                index += 1 
-            # Yield lines that we have collected so far, but first yield 
-            # the user's separator. 
-            if index > context: 
-                yield None, None, None 
-                lines_to_write = context 
-            else: 
-                lines_to_write = index 
-                index = 0 
-            while(lines_to_write): 
-                i = index % context 
-                index += 1 
-                yield contextLines[i] 
-                lines_to_write -= 1 
-            # Now yield the context lines after the change 
-            lines_to_write = context-1 
-            try: 
-                while(lines_to_write): 
-                    from_line, to_line, found_diff = next(line_pair_iterator) 
-                    # If another change within the context, extend the context 
-                    if found_diff: 
-                        lines_to_write = context-1 
-                    else: 
-                        lines_to_write -= 1 
-                    yield from_line, to_line, found_diff 
-            except StopIteration: 
-                # Catch exception from next() and return normally 
-                return 
- 
- 
-_file_template = """ 
-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
-          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
- 
-<html> 
- 
-<head> 
-    <meta http-equiv="Content-Type" 
-          content="text/html; charset=%(charset)s" /> 
-    <title></title> 
-    <style type="text/css">%(styles)s 
-    </style> 
-</head> 
- 
-<body> 
-    %(table)s%(legend)s 
-</body> 
- 
-</html>""" 
- 
-_styles = """ 
-        table.diff {font-family:Courier; border:medium;} 
-        .diff_header {background-color:#e0e0e0} 
-        td.diff_header {text-align:right} 
-        .diff_next {background-color:#c0c0c0} 
-        .diff_add {background-color:#aaffaa} 
-        .diff_chg {background-color:#ffff77} 
-        .diff_sub {background-color:#ffaaaa}""" 
- 
-_table_template = """ 
-    <table class="diff" id="difflib_chg_%(prefix)s_top" 
-           cellspacing="0" cellpadding="0" rules="groups" > 
-        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup> 
-        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup> 
-        %(header_row)s 
-        <tbody> 
-%(data_rows)s        </tbody> 
-    </table>""" 
- 
-_legend = """ 
-    <table class="diff" summary="Legends"> 
-        <tr> <th colspan="2"> Legends </th> </tr> 
-        <tr> <td> <table border="" summary="Colors"> 
-                      <tr><th> Colors </th> </tr> 
-                      <tr><td class="diff_add">&nbsp;Added&nbsp;</td></tr> 
-                      <tr><td class="diff_chg">Changed</td> </tr> 
-                      <tr><td class="diff_sub">Deleted</td> </tr> 
-                  </table></td> 
-             <td> <table border="" summary="Links"> 
-                      <tr><th colspan="2"> Links </th> </tr> 
-                      <tr><td>(f)irst change</td> </tr> 
-                      <tr><td>(n)ext change</td> </tr> 
-                      <tr><td>(t)op</td> </tr> 
-                  </table></td> </tr> 
-    </table>""" 
- 
-class HtmlDiff(object): 
-    """For producing HTML side by side comparison with change highlights. 
- 
-    This class can be used to create an HTML table (or a complete HTML file 
-    containing the table) showing a side by side, line by line comparison 
-    of text with inter-line and intra-line change highlights.  The table can 
-    be generated in either full or contextual difference mode. 
- 
-    The following methods are provided for HTML generation: 
- 
-    make_table -- generates HTML for a single side by side table 
-    make_file -- generates complete HTML file with a single side by side table 
- 
-    See tools/scripts/diff.py for an example usage of this class. 
-    """ 
- 
-    _file_template = _file_template 
-    _styles = _styles 
-    _table_template = _table_template 
-    _legend = _legend 
-    _default_prefix = 0 
- 
-    def __init__(self,tabsize=8,wrapcolumn=None,linejunk=None, 
-                 charjunk=IS_CHARACTER_JUNK): 
-        """HtmlDiff instance initializer 
- 
-        Arguments: 
-        tabsize -- tab stop spacing, defaults to 8. 
-        wrapcolumn -- column number where lines are broken and wrapped, 
-            defaults to None where lines are not wrapped. 
-        linejunk,charjunk -- keyword arguments passed into ndiff() (used by 
-            HtmlDiff() to generate the side by side HTML differences).  See 
-            ndiff() documentation for argument default values and descriptions. 
-        """ 
-        self._tabsize = tabsize 
-        self._wrapcolumn = wrapcolumn 
-        self._linejunk = linejunk 
-        self._charjunk = charjunk 
- 
-    def make_file(self, fromlines, tolines, fromdesc='', todesc='', 
-                  context=False, numlines=5, *, charset='utf-8'): 
-        """Returns HTML file of side by side comparison with change highlights 
- 
-        Arguments: 
-        fromlines -- list of "from" lines 
-        tolines -- list of "to" lines 
-        fromdesc -- "from" file column header string 
-        todesc -- "to" file column header string 
-        context -- set to True for contextual differences (defaults to False 
-            which shows full differences). 
-        numlines -- number of context lines.  When context is set True, 
-            controls number of lines displayed before and after the change. 
-            When context is False, controls the number of lines to place 
-            the "next" link anchors before the next change (so click of 
-            "next" link jumps to just before the change). 
-        charset -- charset of the HTML document 
-        """ 
- 
-        return (self._file_template % dict( 
-            styles=self._styles, 
-            legend=self._legend, 
-            table=self.make_table(fromlines, tolines, fromdesc, todesc, 
-                                  context=context, numlines=numlines), 
-            charset=charset 
-        )).encode(charset, 'xmlcharrefreplace').decode(charset) 
- 
-    def _tab_newline_replace(self,fromlines,tolines): 
-        """Returns from/to line lists with tabs expanded and newlines removed. 
- 
-        Instead of tab characters being replaced by the number of spaces 
-        needed to fill in to the next tab stop, this function will fill 
-        the space with tab characters.  This is done so that the difference 
-        algorithms can identify changes in a file when tabs are replaced by 
-        spaces and vice versa.  At the end of the HTML generation, the tab 
-        characters will be replaced with a nonbreakable space. 
-        """ 
-        def expand_tabs(line): 
-            # hide real spaces 
-            line = line.replace(' ','\0') 
-            # expand tabs into spaces 
-            line = line.expandtabs(self._tabsize) 
-            # replace spaces from expanded tabs back into tab characters 
-            # (we'll replace them with markup after we do differencing) 
-            line = line.replace(' ','\t') 
-            return line.replace('\0',' ').rstrip('\n') 
-        fromlines = [expand_tabs(line) for line in fromlines] 
-        tolines = [expand_tabs(line) for line in tolines] 
-        return fromlines,tolines 
- 
-    def _split_line(self,data_list,line_num,text): 
-        """Builds list of text lines by splitting text lines at wrap point 
- 
-        This function will determine if the input text line needs to be 
-        wrapped (split) into separate lines.  If so, the first wrap point 
-        will be determined and the first line appended to the output 
-        text line list.  This function is used recursively to handle 
-        the second part of the split line to further split it. 
-        """ 
-        # if blank line or context separator, just add it to the output list 
-        if not line_num: 
-            data_list.append((line_num,text)) 
-            return 
- 
-        # if line text doesn't need wrapping, just add it to the output list 
-        size = len(text) 
-        max = self._wrapcolumn 
-        if (size <= max) or ((size -(text.count('\0')*3)) <= max): 
-            data_list.append((line_num,text)) 
-            return 
- 
-        # scan text looking for the wrap point, keeping track if the wrap 
-        # point is inside markers 
-        i = 0 
-        n = 0 
-        mark = '' 
-        while n < max and i < size: 
-            if text[i] == '\0': 
-                i += 1 
-                mark = text[i] 
-                i += 1 
-            elif text[i] == '\1': 
-                i += 1 
-                mark = '' 
-            else: 
-                i += 1 
-                n += 1 
- 
-        # wrap point is inside text, break it up into separate lines 
-        line1 = text[:i] 
-        line2 = text[i:] 
- 
-        # if wrap point is inside markers, place end marker at end of first 
-        # line and start marker at beginning of second line because each 
-        # line will have its own table tag markup around it. 
-        if mark: 
-            line1 = line1 + '\1' 
-            line2 = '\0' + mark + line2 
- 
-        # tack on first line onto the output list 
-        data_list.append((line_num,line1)) 
- 
-        # use this routine again to wrap the remaining text 
-        self._split_line(data_list,'>',line2) 
- 
-    def _line_wrapper(self,diffs): 
-        """Returns iterator that splits (wraps) mdiff text lines""" 
- 
-        # pull from/to data and flags from mdiff iterator 
-        for fromdata,todata,flag in diffs: 
-            # check for context separators and pass them through 
-            if flag is None: 
-                yield fromdata,todata,flag 
-                continue 
-            (fromline,fromtext),(toline,totext) = fromdata,todata 
-            # for each from/to line split it at the wrap column to form 
-            # list of text lines. 
-            fromlist,tolist = [],[] 
-            self._split_line(fromlist,fromline,fromtext) 
-            self._split_line(tolist,toline,totext) 
-            # yield from/to line in pairs inserting blank lines as 
-            # necessary when one side has more wrapped lines 
-            while fromlist or tolist: 
-                if fromlist: 
-                    fromdata = fromlist.pop(0) 
-                else: 
-                    fromdata = ('',' ') 
-                if tolist: 
-                    todata = tolist.pop(0) 
-                else: 
-                    todata = ('',' ') 
-                yield fromdata,todata,flag 
- 
-    def _collect_lines(self,diffs): 
-        """Collects mdiff output into separate lists 
- 
-        Before storing the mdiff from/to data into a list, it is converted 
-        into a single line of text with HTML markup. 
-        """ 
- 
-        fromlist,tolist,flaglist = [],[],[] 
-        # pull from/to data and flags from mdiff style iterator 
-        for fromdata,todata,flag in diffs: 
-            try: 
-                # store HTML markup of the lines into the lists 
-                fromlist.append(self._format_line(0,flag,*fromdata)) 
-                tolist.append(self._format_line(1,flag,*todata)) 
-            except TypeError: 
-                # exceptions occur for lines where context separators go 
-                fromlist.append(None) 
-                tolist.append(None) 
-            flaglist.append(flag) 
-        return fromlist,tolist,flaglist 
- 
-    def _format_line(self,side,flag,linenum,text): 
-        """Returns HTML markup of "from" / "to" text lines 
- 
-        side -- 0 or 1 indicating "from" or "to" text 
-        flag -- indicates if difference on line 
-        linenum -- line number (used for line number column) 
-        text -- line text to be marked up 
-        """ 
-        try: 
-            linenum = '%d' % linenum 
-            id = ' id="%s%s"' % (self._prefix[side],linenum) 
-        except TypeError: 
-            # handle blank lines where linenum is '>' or '' 
-            id = '' 
-        # replace those things that would get confused with HTML symbols 
-        text=text.replace("&","&amp;").replace(">","&gt;").replace("<","&lt;") 
- 
-        # make space non-breakable so they don't get compressed or line wrapped 
-        text = text.replace(' ','&nbsp;').rstrip() 
- 
-        return '<td class="diff_header"%s>%s</td><td nowrap="nowrap">%s</td>' \ 
-               % (id,linenum,text) 
- 
-    def _make_prefix(self): 
-        """Create unique anchor prefixes""" 
- 
-        # Generate a unique anchor prefix so multiple tables 
-        # can exist on the same HTML page without conflicts. 
-        fromprefix = "from%d_" % HtmlDiff._default_prefix 
-        toprefix = "to%d_" % HtmlDiff._default_prefix 
-        HtmlDiff._default_prefix += 1 
-        # store prefixes so line format method has access 
-        self._prefix = [fromprefix,toprefix] 
- 
-    def _convert_flags(self,fromlist,tolist,flaglist,context,numlines): 
-        """Makes list of "next" links""" 
- 
-        # all anchor names will be generated using the unique "to" prefix 
-        toprefix = self._prefix[1] 
- 
-        # process change flags, generating middle column of next anchors/links 
-        next_id = ['']*len(flaglist) 
-        next_href = ['']*len(flaglist) 
-        num_chg, in_change = 0, False 
-        last = 0 
-        for i,flag in enumerate(flaglist): 
-            if flag: 
-                if not in_change: 
-                    in_change = True 
-                    last = i 
-                    # at the beginning of a change, drop an anchor a few lines 
-                    # (the context lines) before the change for the previous 
-                    # link 
-                    i = max([0,i-numlines]) 
-                    next_id[i] = ' id="difflib_chg_%s_%d"' % (toprefix,num_chg) 
-                    # at the beginning of a change, drop a link to the next 
-                    # change 
-                    num_chg += 1 
-                    next_href[last] = '<a href="#difflib_chg_%s_%d">n</a>' % ( 
-                         toprefix,num_chg) 
-            else: 
-                in_change = False 
-        # check for cases where there is no content to avoid exceptions 
-        if not flaglist: 
-            flaglist = [False] 
-            next_id = [''] 
-            next_href = [''] 
-            last = 0 
-            if context: 
-                fromlist = ['<td></td><td>&nbsp;No Differences Found&nbsp;</td>'] 
-                tolist = fromlist 
-            else: 
-                fromlist = tolist = ['<td></td><td>&nbsp;Empty File&nbsp;</td>'] 
-        # if not a change on first line, drop a link 
-        if not flaglist[0]: 
-            next_href[0] = '<a href="#difflib_chg_%s_0">f</a>' % toprefix 
-        # redo the last link to link to the top 
-        next_href[last] = '<a href="#difflib_chg_%s_top">t</a>' % (toprefix) 
- 
-        return fromlist,tolist,flaglist,next_href,next_id 
- 
-    def make_table(self,fromlines,tolines,fromdesc='',todesc='',context=False, 
-                   numlines=5): 
-        """Returns HTML table of side by side comparison with change highlights 
- 
-        Arguments: 
-        fromlines -- list of "from" lines 
-        tolines -- list of "to" lines 
-        fromdesc -- "from" file column header string 
-        todesc -- "to" file column header string 
-        context -- set to True for contextual differences (defaults to False 
-            which shows full differences). 
-        numlines -- number of context lines.  When context is set True, 
-            controls number of lines displayed before and after the change. 
-            When context is False, controls the number of lines to place 
-            the "next" link anchors before the next change (so click of 
-            "next" link jumps to just before the change). 
-        """ 
- 
-        # make unique anchor prefixes so that multiple tables may exist 
-        # on the same page without conflict. 
-        self._make_prefix() 
- 
-        # change tabs to spaces before it gets more difficult after we insert 
-        # markup 
-        fromlines,tolines = self._tab_newline_replace(fromlines,tolines) 
- 
-        # create diffs iterator which generates side by side from/to data 
-        if context: 
-            context_lines = numlines 
-        else: 
-            context_lines = None 
-        diffs = _mdiff(fromlines,tolines,context_lines,linejunk=self._linejunk, 
-                      charjunk=self._charjunk) 
- 
-        # set up iterator to wrap lines that exceed desired width 
-        if self._wrapcolumn: 
-            diffs = self._line_wrapper(diffs) 
- 
-        # collect up from/to lines and flags into lists (also format the lines) 
-        fromlist,tolist,flaglist = self._collect_lines(diffs) 
- 
-        # process change flags, generating middle column of next anchors/links 
-        fromlist,tolist,flaglist,next_href,next_id = self._convert_flags( 
-            fromlist,tolist,flaglist,context,numlines) 
- 
-        s = [] 
-        fmt = '            <tr><td class="diff_next"%s>%s</td>%s' + \ 
-              '<td class="diff_next">%s</td>%s</tr>\n' 
-        for i in range(len(flaglist)): 
-            if flaglist[i] is None: 
-                # mdiff yields None on separator lines skip the bogus ones 
-                # generated for the first line 
-                if i > 0: 
-                    s.append('        </tbody>        \n        <tbody>\n') 
-            else: 
-                s.append( fmt % (next_id[i],next_href[i],fromlist[i], 
-                                           next_href[i],tolist[i])) 
-        if fromdesc or todesc: 
-            header_row = '<thead><tr>%s%s%s%s</tr></thead>' % ( 
-                '<th class="diff_next"><br /></th>', 
-                '<th colspan="2" class="diff_header">%s</th>' % fromdesc, 
-                '<th class="diff_next"><br /></th>', 
-                '<th colspan="2" class="diff_header">%s</th>' % todesc) 
-        else: 
-            header_row = '' 
- 
-        table = self._table_template % dict( 
-            data_rows=''.join(s), 
-            header_row=header_row, 
-            prefix=self._prefix[1]) 
- 
-        return table.replace('\0+','<span class="diff_add">'). \ 
-                     replace('\0-','<span class="diff_sub">'). \ 
-                     replace('\0^','<span class="diff_chg">'). \ 
-                     replace('\1','</span>'). \ 
-                     replace('\t','&nbsp;') 
- 
-del re 
- 
-def restore(delta, which): 
-    r""" 
-    Generate one of the two sequences that generated a delta. 
- 
-    Given a `delta` produced by `Differ.compare()` or `ndiff()`, extract 
-    lines originating from file 1 or 2 (parameter `which`), stripping off line 
-    prefixes. 
- 
-    Examples: 
- 
-    >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(keepends=True), 
-    ...              'ore\ntree\nemu\n'.splitlines(keepends=True)) 
-    >>> diff = list(diff) 
-    >>> print(''.join(restore(diff, 1)), end="") 
-    one 
-    two 
-    three 
-    >>> print(''.join(restore(diff, 2)), end="") 
-    ore 
-    tree 
-    emu 
-    """ 
-    try: 
-        tag = {1: "- ", 2: "+ "}[int(which)] 
-    except KeyError: 
-        raise ValueError('unknown delta choice (must be 1 or 2): %r' 
-                           % which) from None 
-    prefixes = ("  ", tag) 
-    for line in delta: 
-        if line[:2] in prefixes: 
-            yield line[2:] 
- 
-def _test(): 
-    import doctest, difflib 
-    return doctest.testmod(difflib) 
- 
-if __name__ == "__main__": 
-    _test() 
+
+    Examples:
+
+    >>> IS_CHARACTER_JUNK(' ')
+    True
+    >>> IS_CHARACTER_JUNK('\t')
+    True
+    >>> IS_CHARACTER_JUNK('\n')
+    False
+    >>> IS_CHARACTER_JUNK('x')
+    False
+    """
+
+    return ch in ws
+
+
+########################################################################
+###  Unified Diff
+########################################################################
+
+def _format_range_unified(start, stop):
+    'Convert range to the "ed" format'
+    # Per the diff spec at http://www.unix.org/single_unix_specification/
+    beginning = start + 1     # lines start numbering with one
+    length = stop - start
+    if length == 1:
+        return '{}'.format(beginning)
+    if not length:
+        beginning -= 1        # empty ranges begin at line just before the range
+    return '{},{}'.format(beginning, length)
+
+def unified_diff(a, b, fromfile='', tofile='', fromfiledate='',
+                 tofiledate='', n=3, lineterm='\n'):
+    r"""
+    Compare two sequences of lines; generate the delta as a unified diff.
+
+    Unified diffs are a compact way of showing line changes and a few
+    lines of context.  The number of context lines is set by 'n' which
+    defaults to three.
+
+    By default, the diff control lines (those with ---, +++, or @@) are
+    created with a trailing newline.  This is helpful so that inputs
+    created from file.readlines() result in diffs that are suitable for
+    file.writelines() since both the inputs and outputs have trailing
+    newlines.
+
+    For inputs that do not have trailing newlines, set the lineterm
+    argument to "" so that the output will be uniformly newline free.
+
+    The unidiff format normally has a header for filenames and modification
+    times.  Any or all of these may be specified using strings for
+    'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.
+    The modification times are normally expressed in the ISO 8601 format.
+
+    Example:
+
+    >>> for line in unified_diff('one two three four'.split(),
+    ...             'zero one tree four'.split(), 'Original', 'Current',
+    ...             '2005-01-26 23:30:50', '2010-04-02 10:20:52',
+    ...             lineterm=''):
+    ...     print(line)                 # doctest: +NORMALIZE_WHITESPACE
+    --- Original        2005-01-26 23:30:50
+    +++ Current         2010-04-02 10:20:52
+    @@ -1,4 +1,4 @@
+    +zero
+     one
+    -two
+    -three
+    +tree
+     four
+    """
+
+    _check_types(a, b, fromfile, tofile, fromfiledate, tofiledate, lineterm)
+    started = False
+    for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
+        if not started:
+            started = True
+            fromdate = '\t{}'.format(fromfiledate) if fromfiledate else ''
+            todate = '\t{}'.format(tofiledate) if tofiledate else ''
+            yield '--- {}{}{}'.format(fromfile, fromdate, lineterm)
+            yield '+++ {}{}{}'.format(tofile, todate, lineterm)
+
+        first, last = group[0], group[-1]
+        file1_range = _format_range_unified(first[1], last[2])
+        file2_range = _format_range_unified(first[3], last[4])
+        yield '@@ -{} +{} @@{}'.format(file1_range, file2_range, lineterm)
+
+        for tag, i1, i2, j1, j2 in group:
+            if tag == 'equal':
+                for line in a[i1:i2]:
+                    yield ' ' + line
+                continue
+            if tag in {'replace', 'delete'}:
+                for line in a[i1:i2]:
+                    yield '-' + line
+            if tag in {'replace', 'insert'}:
+                for line in b[j1:j2]:
+                    yield '+' + line
+
+
+########################################################################
+###  Context Diff
+########################################################################
+
+def _format_range_context(start, stop):
+    'Convert range to the "ed" format'
+    # Per the diff spec at http://www.unix.org/single_unix_specification/
+    beginning = start + 1     # lines start numbering with one
+    length = stop - start
+    if not length:
+        beginning -= 1        # empty ranges begin at line just before the range
+    if length <= 1:
+        return '{}'.format(beginning)
+    return '{},{}'.format(beginning, beginning + length - 1)
+
+# See http://www.unix.org/single_unix_specification/
+def context_diff(a, b, fromfile='', tofile='',
+                 fromfiledate='', tofiledate='', n=3, lineterm='\n'):
+    r"""
+    Compare two sequences of lines; generate the delta as a context diff.
+
+    Context diffs are a compact way of showing line changes and a few
+    lines of context.  The number of context lines is set by 'n' which
+    defaults to three.
+
+    By default, the diff control lines (those with *** or ---) are
+    created with a trailing newline.  This is helpful so that inputs
+    created from file.readlines() result in diffs that are suitable for
+    file.writelines() since both the inputs and outputs have trailing
+    newlines.
+
+    For inputs that do not have trailing newlines, set the lineterm
+    argument to "" so that the output will be uniformly newline free.
+
+    The context diff format normally has a header for filenames and
+    modification times.  Any or all of these may be specified using
+    strings for 'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.
+    The modification times are normally expressed in the ISO 8601 format.
+    If not specified, the strings default to blanks.
+
+    Example:
+
+    >>> print(''.join(context_diff('one\ntwo\nthree\nfour\n'.splitlines(True),
+    ...       'zero\none\ntree\nfour\n'.splitlines(True), 'Original', 'Current')),
+    ...       end="")
+    *** Original
+    --- Current
+    ***************
+    *** 1,4 ****
+      one
+    ! two
+    ! three
+      four
+    --- 1,4 ----
+    + zero
+      one
+    ! tree
+      four
+    """
+
+    _check_types(a, b, fromfile, tofile, fromfiledate, tofiledate, lineterm)
+    prefix = dict(insert='+ ', delete='- ', replace='! ', equal='  ')
+    started = False
+    for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
+        if not started:
+            started = True
+            fromdate = '\t{}'.format(fromfiledate) if fromfiledate else ''
+            todate = '\t{}'.format(tofiledate) if tofiledate else ''
+            yield '*** {}{}{}'.format(fromfile, fromdate, lineterm)
+            yield '--- {}{}{}'.format(tofile, todate, lineterm)
+
+        first, last = group[0], group[-1]
+        yield '***************' + lineterm
+
+        file1_range = _format_range_context(first[1], last[2])
+        yield '*** {} ****{}'.format(file1_range, lineterm)
+
+        if any(tag in {'replace', 'delete'} for tag, _, _, _, _ in group):
+            for tag, i1, i2, _, _ in group:
+                if tag != 'insert':
+                    for line in a[i1:i2]:
+                        yield prefix[tag] + line
+
+        file2_range = _format_range_context(first[3], last[4])
+        yield '--- {} ----{}'.format(file2_range, lineterm)
+
+        if any(tag in {'replace', 'insert'} for tag, _, _, _, _ in group):
+            for tag, _, _, j1, j2 in group:
+                if tag != 'delete':
+                    for line in b[j1:j2]:
+                        yield prefix[tag] + line
+
+def _check_types(a, b, *args):
+    # Checking types is weird, but the alternative is garbled output when
+    # someone passes mixed bytes and str to {unified,context}_diff(). E.g.
+    # without this check, passing filenames as bytes results in output like
+    #   --- b'oldfile.txt'
+    #   +++ b'newfile.txt'
+    # because of how str.format() incorporates bytes objects.
+    if a and not isinstance(a[0], str):
+        raise TypeError('lines to compare must be str, not %s (%r)' %
+                        (type(a[0]).__name__, a[0]))
+    if b and not isinstance(b[0], str):
+        raise TypeError('lines to compare must be str, not %s (%r)' %
+                        (type(b[0]).__name__, b[0]))
+    for arg in args:
+        if not isinstance(arg, str):
+            raise TypeError('all arguments must be str, not: %r' % (arg,))
+
+def diff_bytes(dfunc, a, b, fromfile=b'', tofile=b'',
+               fromfiledate=b'', tofiledate=b'', n=3, lineterm=b'\n'):
+    r"""
+    Compare `a` and `b`, two sequences of lines represented as bytes rather
+    than str. This is a wrapper for `dfunc`, which is typically either
+    unified_diff() or context_diff(). Inputs are losslessly converted to
+    strings so that `dfunc` only has to worry about strings, and encoded
+    back to bytes on return. This is necessary to compare files with
+    unknown or inconsistent encoding. All other inputs (except `n`) must be
+    bytes rather than str.
+    """
+    def decode(s):
+        try:
+            return s.decode('ascii', 'surrogateescape')
+        except AttributeError as err:
+            msg = ('all arguments must be bytes, not %s (%r)' %
+                   (type(s).__name__, s))
+            raise TypeError(msg) from err
+    a = list(map(decode, a))
+    b = list(map(decode, b))
+    fromfile = decode(fromfile)
+    tofile = decode(tofile)
+    fromfiledate = decode(fromfiledate)
+    tofiledate = decode(tofiledate)
+    lineterm = decode(lineterm)
+
+    lines = dfunc(a, b, fromfile, tofile, fromfiledate, tofiledate, n, lineterm)
+    for line in lines:
+        yield line.encode('ascii', 'surrogateescape')
+
+def ndiff(a, b, linejunk=None, charjunk=IS_CHARACTER_JUNK):
+    r"""
+    Compare `a` and `b` (lists of strings); return a `Differ`-style delta.
+
+    Optional keyword parameters `linejunk` and `charjunk` are for filter
+    functions, or can be None:
+
+    - linejunk: A function that should accept a single string argument and
+      return true iff the string is junk.  The default is None, and is
+      recommended; the underlying SequenceMatcher class has an adaptive
+      notion of "noise" lines.
+
+    - charjunk: A function that accepts a character (string of length
+      1), and returns true iff the character is junk. The default is
+      the module-level function IS_CHARACTER_JUNK, which filters out
+      whitespace characters (a blank or tab; note: it's a bad idea to
+      include newline in this!).
+
+    Tools/scripts/ndiff.py is a command-line front-end to this function.
+
+    Example:
+
+    >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(keepends=True),
+    ...              'ore\ntree\nemu\n'.splitlines(keepends=True))
+    >>> print(''.join(diff), end="")
+    - one
+    ?  ^
+    + ore
+    ?  ^
+    - two
+    - three
+    ?  -
+    + tree
+    + emu
+    """
+    return Differ(linejunk, charjunk).compare(a, b)
+
+def _mdiff(fromlines, tolines, context=None, linejunk=None,
+           charjunk=IS_CHARACTER_JUNK):
+    r"""Returns generator yielding marked up from/to side by side differences.
+
+    Arguments:
+    fromlines -- list of text lines to compared to tolines
+    tolines -- list of text lines to be compared to fromlines
+    context -- number of context lines to display on each side of difference,
+               if None, all from/to text lines will be generated.
+    linejunk -- passed on to ndiff (see ndiff documentation)
+    charjunk -- passed on to ndiff (see ndiff documentation)
+
+    This function returns an iterator which returns a tuple:
+    (from line tuple, to line tuple, boolean flag)
+
+    from/to line tuple -- (line num, line text)
+        line num -- integer or None (to indicate a context separation)
+        line text -- original line text with following markers inserted:
+            '\0+' -- marks start of added text
+            '\0-' -- marks start of deleted text
+            '\0^' -- marks start of changed text
+            '\1' -- marks end of added/deleted/changed text
+
+    boolean flag -- None indicates context separation, True indicates
+        either "from" or "to" line contains a change, otherwise False.
+
+    This function/iterator was originally developed to generate side by side
+    file difference for making HTML pages (see HtmlDiff class for example
+    usage).
+
+    Note, this function utilizes the ndiff function to generate the side by
+    side difference markup.  Optional ndiff arguments may be passed to this
+    function and they in turn will be passed to ndiff.
+    """
+    import re
+
+    # regular expression for finding intraline change indices
+    change_re = re.compile(r'(\++|\-+|\^+)')
+
+    # create the difference iterator to generate the differences
+    diff_lines_iterator = ndiff(fromlines,tolines,linejunk,charjunk)
+
+    def _make_line(lines, format_key, side, num_lines=[0,0]):
+        """Returns line of text with user's change markup and line formatting.
+
+        lines -- list of lines from the ndiff generator to produce a line of
+                 text from.  When producing the line of text to return, the
+                 lines used are removed from this list.
+        format_key -- '+' return first line in list with "add" markup around
+                          the entire line.
+                      '-' return first line in list with "delete" markup around
+                          the entire line.
+                      '?' return first line in list with add/delete/change
+                          intraline markup (indices obtained from second line)
+                      None return first line in list with no markup
+        side -- indice into the num_lines list (0=from,1=to)
+        num_lines -- from/to current line number.  This is NOT intended to be a
+                     passed parameter.  It is present as a keyword argument to
+                     maintain memory of the current line numbers between calls
+                     of this function.
+
+        Note, this function is purposefully not defined at the module scope so
+        that data it needs from its parent function (within whose context it
+        is defined) does not need to be of module scope.
+        """
+        num_lines[side] += 1
+        # Handle case where no user markup is to be added, just return line of
+        # text with user's line format to allow for usage of the line number.
+        if format_key is None:
+            return (num_lines[side],lines.pop(0)[2:])
+        # Handle case of intraline changes
+        if format_key == '?':
+            text, markers = lines.pop(0), lines.pop(0)
+            # find intraline changes (store change type and indices in tuples)
+            sub_info = []
+            def record_sub_info(match_object,sub_info=sub_info):
+                sub_info.append([match_object.group(1)[0],match_object.span()])
+                return match_object.group(1)
+            change_re.sub(record_sub_info,markers)
+            # process each tuple inserting our special marks that won't be
+            # noticed by an xml/html escaper.
+            for key,(begin,end) in reversed(sub_info):
+                text = text[0:begin]+'\0'+key+text[begin:end]+'\1'+text[end:]
+            text = text[2:]
+        # Handle case of add/delete entire line
+        else:
+            text = lines.pop(0)[2:]
+            # if line of text is just a newline, insert a space so there is
+            # something for the user to highlight and see.
+            if not text:
+                text = ' '
+            # insert marks that won't be noticed by an xml/html escaper.
+            text = '\0' + format_key + text + '\1'
+        # Return line of text, first allow user's line formatter to do its
+        # thing (such as adding the line number) then replace the special
+        # marks with what the user's change markup.
+        return (num_lines[side],text)
+
+    def _line_iterator():
+        """Yields from/to lines of text with a change indication.
+
+        This function is an iterator.  It itself pulls lines from a
+        differencing iterator, processes them and yields them.  When it can
+        it yields both a "from" and a "to" line, otherwise it will yield one
+        or the other.  In addition to yielding the lines of from/to text, a
+        boolean flag is yielded to indicate if the text line(s) have
+        differences in them.
+
+        Note, this function is purposefully not defined at the module scope so
+        that data it needs from its parent function (within whose context it
+        is defined) does not need to be of module scope.
+        """
+        lines = []
+        num_blanks_pending, num_blanks_to_yield = 0, 0
+        while True:
+            # Load up next 4 lines so we can look ahead, create strings which
+            # are a concatenation of the first character of each of the 4 lines
+            # so we can do some very readable comparisons.
+            while len(lines) < 4:
+                lines.append(next(diff_lines_iterator, 'X'))
+            s = ''.join([line[0] for line in lines])
+            if s.startswith('X'):
+                # When no more lines, pump out any remaining blank lines so the
+                # corresponding add/delete lines get a matching blank line so
+                # all line pairs get yielded at the next level.
+                num_blanks_to_yield = num_blanks_pending
+            elif s.startswith('-?+?'):
+                # simple intraline change
+                yield _make_line(lines,'?',0), _make_line(lines,'?',1), True
+                continue
+            elif s.startswith('--++'):
+                # in delete block, add block coming: we do NOT want to get
+                # caught up on blank lines yet, just process the delete line
+                num_blanks_pending -= 1
+                yield _make_line(lines,'-',0), None, True
+                continue
+            elif s.startswith(('--?+', '--+', '- ')):
+                # in delete block and see an intraline change or unchanged line
+                # coming: yield the delete line and then blanks
+                from_line,to_line = _make_line(lines,'-',0), None
+                num_blanks_to_yield,num_blanks_pending = num_blanks_pending-1,0
+            elif s.startswith('-+?'):
+                # intraline change
+                yield _make_line(lines,None,0), _make_line(lines,'?',1), True
+                continue
+            elif s.startswith('-?+'):
+                # intraline change
+                yield _make_line(lines,'?',0), _make_line(lines,None,1), True
+                continue
+            elif s.startswith('-'):
+                # delete FROM line
+                num_blanks_pending -= 1
+                yield _make_line(lines,'-',0), None, True
+                continue
+            elif s.startswith('+--'):
+                # in add block, delete block coming: we do NOT want to get
+                # caught up on blank lines yet, just process the add line
+                num_blanks_pending += 1
+                yield None, _make_line(lines,'+',1), True
+                continue
+            elif s.startswith(('+ ', '+-')):
+                # will be leaving an add block: yield blanks then add line
+                from_line, to_line = None, _make_line(lines,'+',1)
+                num_blanks_to_yield,num_blanks_pending = num_blanks_pending+1,0
+            elif s.startswith('+'):
+                # inside an add block, yield the add line
+                num_blanks_pending += 1
+                yield None, _make_line(lines,'+',1), True
+                continue
+            elif s.startswith(' '):
+                # unchanged text, yield it to both sides
+                yield _make_line(lines[:],None,0),_make_line(lines,None,1),False
+                continue
+            # Catch up on the blank lines so when we yield the next from/to
+            # pair, they are lined up.
+            while(num_blanks_to_yield < 0):
+                num_blanks_to_yield += 1
+                yield None,('','\n'),True
+            while(num_blanks_to_yield > 0):
+                num_blanks_to_yield -= 1
+                yield ('','\n'),None,True
+            if s.startswith('X'):
+                return
+            else:
+                yield from_line,to_line,True
+
+    def _line_pair_iterator():
+        """Yields from/to lines of text with a change indication.
+
+        This function is an iterator.  It itself pulls lines from the line
+        iterator.  Its difference from that iterator is that this function
+        always yields a pair of from/to text lines (with the change
+        indication).  If necessary it will collect single from/to lines
+        until it has a matching pair from/to pair to yield.
+
+        Note, this function is purposefully not defined at the module scope so
+        that data it needs from its parent function (within whose context it
+        is defined) does not need to be of module scope.
+        """
+        line_iterator = _line_iterator()
+        fromlines,tolines=[],[]
+        while True:
+            # Collecting lines of text until we have a from/to pair
+            while (len(fromlines)==0 or len(tolines)==0):
+                try:
+                    from_line, to_line, found_diff = next(line_iterator)
+                except StopIteration:
+                    return
+                if from_line is not None:
+                    fromlines.append((from_line,found_diff))
+                if to_line is not None:
+                    tolines.append((to_line,found_diff))
+            # Once we have a pair, remove them from the collection and yield it
+            from_line, fromDiff = fromlines.pop(0)
+            to_line, to_diff = tolines.pop(0)
+            yield (from_line,to_line,fromDiff or to_diff)
+
+    # Handle case where user does not want context differencing, just yield
+    # them up without doing anything else with them.
+    line_pair_iterator = _line_pair_iterator()
+    if context is None:
+        yield from line_pair_iterator
+    # Handle case where user wants context differencing.  We must do some
+    # storage of lines until we know for sure that they are to be yielded.
+    else:
+        context += 1
+        lines_to_write = 0
+        while True:
+            # Store lines up until we find a difference, note use of a
+            # circular queue because we only need to keep around what
+            # we need for context.
+            index, contextLines = 0, [None]*(context)
+            found_diff = False
+            while(found_diff is False):
+                try:
+                    from_line, to_line, found_diff = next(line_pair_iterator)
+                except StopIteration:
+                    return
+                i = index % context
+                contextLines[i] = (from_line, to_line, found_diff)
+                index += 1
+            # Yield lines that we have collected so far, but first yield
+            # the user's separator.
+            if index > context:
+                yield None, None, None
+                lines_to_write = context
+            else:
+                lines_to_write = index
+                index = 0
+            while(lines_to_write):
+                i = index % context
+                index += 1
+                yield contextLines[i]
+                lines_to_write -= 1
+            # Now yield the context lines after the change
+            lines_to_write = context-1
+            try:
+                while(lines_to_write):
+                    from_line, to_line, found_diff = next(line_pair_iterator)
+                    # If another change within the context, extend the context
+                    if found_diff:
+                        lines_to_write = context-1
+                    else:
+                        lines_to_write -= 1
+                    yield from_line, to_line, found_diff
+            except StopIteration:
+                # Catch exception from next() and return normally
+                return
+
+
+_file_template = """
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
+          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+
+<html>
+
+<head>
+    <meta http-equiv="Content-Type"
+          content="text/html; charset=%(charset)s" />
+    <title></title>
+    <style type="text/css">%(styles)s
+    </style>
+</head>
+
+<body>
+    %(table)s%(legend)s
+</body>
+
+</html>"""
+
+_styles = """
+        table.diff {font-family:Courier; border:medium;}
+        .diff_header {background-color:#e0e0e0}
+        td.diff_header {text-align:right}
+        .diff_next {background-color:#c0c0c0}
+        .diff_add {background-color:#aaffaa}
+        .diff_chg {background-color:#ffff77}
+        .diff_sub {background-color:#ffaaaa}"""
+
+_table_template = """
+    <table class="diff" id="difflib_chg_%(prefix)s_top"
+           cellspacing="0" cellpadding="0" rules="groups" >
+        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup>
+        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup>
+        %(header_row)s
+        <tbody>
+%(data_rows)s        </tbody>
+    </table>"""
+
+_legend = """
+    <table class="diff" summary="Legends">
+        <tr> <th colspan="2"> Legends </th> </tr>
+        <tr> <td> <table border="" summary="Colors">
+                      <tr><th> Colors </th> </tr>
+                      <tr><td class="diff_add">&nbsp;Added&nbsp;</td></tr>
+                      <tr><td class="diff_chg">Changed</td> </tr>
+                      <tr><td class="diff_sub">Deleted</td> </tr>
+                  </table></td>
+             <td> <table border="" summary="Links">
+                      <tr><th colspan="2"> Links </th> </tr>
+                      <tr><td>(f)irst change</td> </tr>
+                      <tr><td>(n)ext change</td> </tr>
+                      <tr><td>(t)op</td> </tr>
+                  </table></td> </tr>
+    </table>"""
+
+class HtmlDiff(object):
+    """For producing HTML side by side comparison with change highlights.
+
+    This class can be used to create an HTML table (or a complete HTML file
+    containing the table) showing a side by side, line by line comparison
+    of text with inter-line and intra-line change highlights.  The table can
+    be generated in either full or contextual difference mode.
+
+    The following methods are provided for HTML generation:
+
+    make_table -- generates HTML for a single side by side table
+    make_file -- generates complete HTML file with a single side by side table
+
+    See tools/scripts/diff.py for an example usage of this class.
+    """
+
+    _file_template = _file_template
+    _styles = _styles
+    _table_template = _table_template
+    _legend = _legend
+    _default_prefix = 0
+
+    def __init__(self,tabsize=8,wrapcolumn=None,linejunk=None,
+                 charjunk=IS_CHARACTER_JUNK):
+        """HtmlDiff instance initializer
+
+        Arguments:
+        tabsize -- tab stop spacing, defaults to 8.
+        wrapcolumn -- column number where lines are broken and wrapped,
+            defaults to None where lines are not wrapped.
+        linejunk,charjunk -- keyword arguments passed into ndiff() (used by
+            HtmlDiff() to generate the side by side HTML differences).  See
+            ndiff() documentation for argument default values and descriptions.
+        """
+        self._tabsize = tabsize
+        self._wrapcolumn = wrapcolumn
+        self._linejunk = linejunk
+        self._charjunk = charjunk
+
+    def make_file(self, fromlines, tolines, fromdesc='', todesc='',
+                  context=False, numlines=5, *, charset='utf-8'):
+        """Returns HTML file of side by side comparison with change highlights
+
+        Arguments:
+        fromlines -- list of "from" lines
+        tolines -- list of "to" lines
+        fromdesc -- "from" file column header string
+        todesc -- "to" file column header string
+        context -- set to True for contextual differences (defaults to False
+            which shows full differences).
+        numlines -- number of context lines.  When context is set True,
+            controls number of lines displayed before and after the change.
+            When context is False, controls the number of lines to place
+            the "next" link anchors before the next change (so click of
+            "next" link jumps to just before the change).
+        charset -- charset of the HTML document
+        """
+
+        return (self._file_template % dict(
+            styles=self._styles,
+            legend=self._legend,
+            table=self.make_table(fromlines, tolines, fromdesc, todesc,
+                                  context=context, numlines=numlines),
+            charset=charset
+        )).encode(charset, 'xmlcharrefreplace').decode(charset)
+
+    def _tab_newline_replace(self,fromlines,tolines):
+        """Returns from/to line lists with tabs expanded and newlines removed.
+
+        Instead of tab characters being replaced by the number of spaces
+        needed to fill in to the next tab stop, this function will fill
+        the space with tab characters.  This is done so that the difference
+        algorithms can identify changes in a file when tabs are replaced by
+        spaces and vice versa.  At the end of the HTML generation, the tab
+        characters will be replaced with a nonbreakable space.
+        """
+        def expand_tabs(line):
+            # hide real spaces
+            line = line.replace(' ','\0')
+            # expand tabs into spaces
+            line = line.expandtabs(self._tabsize)
+            # replace spaces from expanded tabs back into tab characters
+            # (we'll replace them with markup after we do differencing)
+            line = line.replace(' ','\t')
+            return line.replace('\0',' ').rstrip('\n')
+        fromlines = [expand_tabs(line) for line in fromlines]
+        tolines = [expand_tabs(line) for line in tolines]
+        return fromlines,tolines
+
+    def _split_line(self,data_list,line_num,text):
+        """Builds list of text lines by splitting text lines at wrap point
+
+        This function will determine if the input text line needs to be
+        wrapped (split) into separate lines.  If so, the first wrap point
+        will be determined and the first line appended to the output
+        text line list.  This function is used recursively to handle
+        the second part of the split line to further split it.
+        """
+        # if blank line or context separator, just add it to the output list
+        if not line_num:
+            data_list.append((line_num,text))
+            return
+
+        # if line text doesn't need wrapping, just add it to the output list
+        size = len(text)
+        max = self._wrapcolumn
+        if (size <= max) or ((size -(text.count('\0')*3)) <= max):
+            data_list.append((line_num,text))
+            return
+
+        # scan text looking for the wrap point, keeping track if the wrap
+        # point is inside markers
+        i = 0
+        n = 0
+        mark = ''
+        while n < max and i < size:
+            if text[i] == '\0':
+                i += 1
+                mark = text[i]
+                i += 1
+            elif text[i] == '\1':
+                i += 1
+                mark = ''
+            else:
+                i += 1
+                n += 1
+
+        # wrap point is inside text, break it up into separate lines
+        line1 = text[:i]
+        line2 = text[i:]
+
+        # if wrap point is inside markers, place end marker at end of first
+        # line and start marker at beginning of second line because each
+        # line will have its own table tag markup around it.
+        if mark:
+            line1 = line1 + '\1'
+            line2 = '\0' + mark + line2
+
+        # tack on first line onto the output list
+        data_list.append((line_num,line1))
+
+        # use this routine again to wrap the remaining text
+        self._split_line(data_list,'>',line2)
+
+    def _line_wrapper(self,diffs):
+        """Returns iterator that splits (wraps) mdiff text lines"""
+
+        # pull from/to data and flags from mdiff iterator
+        for fromdata,todata,flag in diffs:
+            # check for context separators and pass them through
+            if flag is None:
+                yield fromdata,todata,flag
+                continue
+            (fromline,fromtext),(toline,totext) = fromdata,todata
+            # for each from/to line split it at the wrap column to form
+            # list of text lines.
+            fromlist,tolist = [],[]
+            self._split_line(fromlist,fromline,fromtext)
+            self._split_line(tolist,toline,totext)
+            # yield from/to line in pairs inserting blank lines as
+            # necessary when one side has more wrapped lines
+            while fromlist or tolist:
+                if fromlist:
+                    fromdata = fromlist.pop(0)
+                else:
+                    fromdata = ('',' ')
+                if tolist:
+                    todata = tolist.pop(0)
+                else:
+                    todata = ('',' ')
+                yield fromdata,todata,flag
+
+    def _collect_lines(self,diffs):
+        """Collects mdiff output into separate lists
+
+        Before storing the mdiff from/to data into a list, it is converted
+        into a single line of text with HTML markup.
+        """
+
+        fromlist,tolist,flaglist = [],[],[]
+        # pull from/to data and flags from mdiff style iterator
+        for fromdata,todata,flag in diffs:
+            try:
+                # store HTML markup of the lines into the lists
+                fromlist.append(self._format_line(0,flag,*fromdata))
+                tolist.append(self._format_line(1,flag,*todata))
+            except TypeError:
+                # exceptions occur for lines where context separators go
+                fromlist.append(None)
+                tolist.append(None)
+            flaglist.append(flag)
+        return fromlist,tolist,flaglist
+
+    def _format_line(self,side,flag,linenum,text):
+        """Returns HTML markup of "from" / "to" text lines
+
+        side -- 0 or 1 indicating "from" or "to" text
+        flag -- indicates if difference on line
+        linenum -- line number (used for line number column)
+        text -- line text to be marked up
+        """
+        try:
+            linenum = '%d' % linenum
+            id = ' id="%s%s"' % (self._prefix[side],linenum)
+        except TypeError:
+            # handle blank lines where linenum is '>' or ''
+            id = ''
+        # replace those things that would get confused with HTML symbols
+        text=text.replace("&","&amp;").replace(">","&gt;").replace("<","&lt;")
+
+        # make space non-breakable so they don't get compressed or line wrapped
+        text = text.replace(' ','&nbsp;').rstrip()
+
+        return '<td class="diff_header"%s>%s</td><td nowrap="nowrap">%s</td>' \
+               % (id,linenum,text)
+
+    def _make_prefix(self):
+        """Create unique anchor prefixes"""
+
+        # Generate a unique anchor prefix so multiple tables
+        # can exist on the same HTML page without conflicts.
+        fromprefix = "from%d_" % HtmlDiff._default_prefix
+        toprefix = "to%d_" % HtmlDiff._default_prefix
+        HtmlDiff._default_prefix += 1
+        # store prefixes so line format method has access
+        self._prefix = [fromprefix,toprefix]
+
+    def _convert_flags(self,fromlist,tolist,flaglist,context,numlines):
+        """Makes list of "next" links"""
+
+        # all anchor names will be generated using the unique "to" prefix
+        toprefix = self._prefix[1]
+
+        # process change flags, generating middle column of next anchors/links
+        next_id = ['']*len(flaglist)
+        next_href = ['']*len(flaglist)
+        num_chg, in_change = 0, False
+        last = 0
+        for i,flag in enumerate(flaglist):
+            if flag:
+                if not in_change:
+                    in_change = True
+                    last = i
+                    # at the beginning of a change, drop an anchor a few lines
+                    # (the context lines) before the change for the previous
+                    # link
+                    i = max([0,i-numlines])
+                    next_id[i] = ' id="difflib_chg_%s_%d"' % (toprefix,num_chg)
+                    # at the beginning of a change, drop a link to the next
+                    # change
+                    num_chg += 1
+                    next_href[last] = '<a href="#difflib_chg_%s_%d">n</a>' % (
+                         toprefix,num_chg)
+            else:
+                in_change = False
+        # check for cases where there is no content to avoid exceptions
+        if not flaglist:
+            flaglist = [False]
+            next_id = ['']
+            next_href = ['']
+            last = 0
+            if context:
+                fromlist = ['<td></td><td>&nbsp;No Differences Found&nbsp;</td>']
+                tolist = fromlist
+            else:
+                fromlist = tolist = ['<td></td><td>&nbsp;Empty File&nbsp;</td>']
+        # if not a change on first line, drop a link
+        if not flaglist[0]:
+            next_href[0] = '<a href="#difflib_chg_%s_0">f</a>' % toprefix
+        # redo the last link to link to the top
+        next_href[last] = '<a href="#difflib_chg_%s_top">t</a>' % (toprefix)
+
+        return fromlist,tolist,flaglist,next_href,next_id
+
+    def make_table(self,fromlines,tolines,fromdesc='',todesc='',context=False,
+                   numlines=5):
+        """Returns HTML table of side by side comparison with change highlights
+
+        Arguments:
+        fromlines -- list of "from" lines
+        tolines -- list of "to" lines
+        fromdesc -- "from" file column header string
+        todesc -- "to" file column header string
+        context -- set to True for contextual differences (defaults to False
+            which shows full differences).
+        numlines -- number of context lines.  When context is set True,
+            controls number of lines displayed before and after the change.
+            When context is False, controls the number of lines to place
+            the "next" link anchors before the next change (so click of
+            "next" link jumps to just before the change).
+        """
+
+        # make unique anchor prefixes so that multiple tables may exist
+        # on the same page without conflict.
+        self._make_prefix()
+
+        # change tabs to spaces before it gets more difficult after we insert
+        # markup
+        fromlines,tolines = self._tab_newline_replace(fromlines,tolines)
+
+        # create diffs iterator which generates side by side from/to data
+        if context:
+            context_lines = numlines
+        else:
+            context_lines = None
+        diffs = _mdiff(fromlines,tolines,context_lines,linejunk=self._linejunk,
+                      charjunk=self._charjunk)
+
+        # set up iterator to wrap lines that exceed desired width
+        if self._wrapcolumn:
+            diffs = self._line_wrapper(diffs)
+
+        # collect up from/to lines and flags into lists (also format the lines)
+        fromlist,tolist,flaglist = self._collect_lines(diffs)
+
+        # process change flags, generating middle column of next anchors/links
+        fromlist,tolist,flaglist,next_href,next_id = self._convert_flags(
+            fromlist,tolist,flaglist,context,numlines)
+
+        s = []
+        fmt = '            <tr><td class="diff_next"%s>%s</td>%s' + \
+              '<td class="diff_next">%s</td>%s</tr>\n'
+        for i in range(len(flaglist)):
+            if flaglist[i] is None:
+                # mdiff yields None on separator lines skip the bogus ones
+                # generated for the first line
+                if i > 0:
+                    s.append('        </tbody>        \n        <tbody>\n')
+            else:
+                s.append( fmt % (next_id[i],next_href[i],fromlist[i],
+                                           next_href[i],tolist[i]))
+        if fromdesc or todesc:
+            header_row = '<thead><tr>%s%s%s%s</tr></thead>' % (
+                '<th class="diff_next"><br /></th>',
+                '<th colspan="2" class="diff_header">%s</th>' % fromdesc,
+                '<th class="diff_next"><br /></th>',
+                '<th colspan="2" class="diff_header">%s</th>' % todesc)
+        else:
+            header_row = ''
+
+        table = self._table_template % dict(
+            data_rows=''.join(s),
+            header_row=header_row,
+            prefix=self._prefix[1])
+
+        return table.replace('\0+','<span class="diff_add">'). \
+                     replace('\0-','<span class="diff_sub">'). \
+                     replace('\0^','<span class="diff_chg">'). \
+                     replace('\1','</span>'). \
+                     replace('\t','&nbsp;')
+
+del re
+
+def restore(delta, which):
+    r"""
+    Generate one of the two sequences that generated a delta.
+
+    Given a `delta` produced by `Differ.compare()` or `ndiff()`, extract
+    lines originating from file 1 or 2 (parameter `which`), stripping off line
+    prefixes.
+
+    Examples:
+
+    >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(keepends=True),
+    ...              'ore\ntree\nemu\n'.splitlines(keepends=True))
+    >>> diff = list(diff)
+    >>> print(''.join(restore(diff, 1)), end="")
+    one
+    two
+    three
+    >>> print(''.join(restore(diff, 2)), end="")
+    ore
+    tree
+    emu
+    """
+    try:
+        tag = {1: "- ", 2: "+ "}[int(which)]
+    except KeyError:
+        raise ValueError('unknown delta choice (must be 1 or 2): %r'
+                           % which) from None
+    prefixes = ("  ", tag)
+    for line in delta:
+        if line[:2] in prefixes:
+            yield line[2:]
+
+def _test():
+    import doctest, difflib
+    return doctest.testmod(difflib)
+
+if __name__ == "__main__":
+    _test()