add ydb deps

1 files changed, 1102 insertions, 0 deletions

diff --git a/contrib/tools/python3/src/Lib/re/_parser.py b/contrib/tools/python3/src/Lib/re/_parser.py
new file mode 100644
index 0000000000..6b715f5403
--- /dev/null
+++ b/contrib/tools/python3/src/Lib/re/_parser.py
@@ -0,0 +1,1102 @@
+#
+# Secret Labs' Regular Expression Engine
+#
+# convert re-style regular expression to sre pattern
+#
+# Copyright (c) 1998-2001 by Secret Labs AB.  All rights reserved.
+#
+# See the __init__.py file for information on usage and redistribution.
+#
+
+"""Internal support module for sre"""
+
+# XXX: show string offset and offending character for all errors
+
+from ._constants import *
+
+SPECIAL_CHARS = ".\\[{()*+?^$|"
+REPEAT_CHARS = "*+?{"
+
+DIGITS = frozenset("0123456789")
+
+OCTDIGITS = frozenset("01234567")
+HEXDIGITS = frozenset("0123456789abcdefABCDEF")
+ASCIILETTERS = frozenset("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
+
+WHITESPACE = frozenset(" \t\n\r\v\f")
+
+_REPEATCODES = frozenset({MIN_REPEAT, MAX_REPEAT, POSSESSIVE_REPEAT})
+_UNITCODES = frozenset({ANY, RANGE, IN, LITERAL, NOT_LITERAL, CATEGORY})
+
+ESCAPES = {
+    r"\a": (LITERAL, ord("\a")),
+    r"\b": (LITERAL, ord("\b")),
+    r"\f": (LITERAL, ord("\f")),
+    r"\n": (LITERAL, ord("\n")),
+    r"\r": (LITERAL, ord("\r")),
+    r"\t": (LITERAL, ord("\t")),
+    r"\v": (LITERAL, ord("\v")),
+    r"\\": (LITERAL, ord("\\"))
+}
+
+CATEGORIES = {
+    r"\A": (AT, AT_BEGINNING_STRING), # start of string
+    r"\b": (AT, AT_BOUNDARY),
+    r"\B": (AT, AT_NON_BOUNDARY),
+    r"\d": (IN, [(CATEGORY, CATEGORY_DIGIT)]),
+    r"\D": (IN, [(CATEGORY, CATEGORY_NOT_DIGIT)]),
+    r"\s": (IN, [(CATEGORY, CATEGORY_SPACE)]),
+    r"\S": (IN, [(CATEGORY, CATEGORY_NOT_SPACE)]),
+    r"\w": (IN, [(CATEGORY, CATEGORY_WORD)]),
+    r"\W": (IN, [(CATEGORY, CATEGORY_NOT_WORD)]),
+    r"\Z": (AT, AT_END_STRING), # end of string
+}
+
+FLAGS = {
+    # standard flags
+    "i": SRE_FLAG_IGNORECASE,
+    "L": SRE_FLAG_LOCALE,
+    "m": SRE_FLAG_MULTILINE,
+    "s": SRE_FLAG_DOTALL,
+    "x": SRE_FLAG_VERBOSE,
+    # extensions
+    "a": SRE_FLAG_ASCII,
+    "t": SRE_FLAG_TEMPLATE,
+    "u": SRE_FLAG_UNICODE,
+}
+
+TYPE_FLAGS = SRE_FLAG_ASCII | SRE_FLAG_LOCALE | SRE_FLAG_UNICODE
+GLOBAL_FLAGS = SRE_FLAG_DEBUG | SRE_FLAG_TEMPLATE
+
+class State:
+    # keeps track of state for parsing
+    def __init__(self):
+        self.flags = 0
+        self.groupdict = {}
+        self.groupwidths = [None]  # group 0
+        self.lookbehindgroups = None
+        self.grouprefpos = {}
+    @property
+    def groups(self):
+        return len(self.groupwidths)
+    def opengroup(self, name=None):
+        gid = self.groups
+        self.groupwidths.append(None)
+        if self.groups > MAXGROUPS:
+            raise error("too many groups")
+        if name is not None:
+            ogid = self.groupdict.get(name, None)
+            if ogid is not None:
+                raise error("redefinition of group name %r as group %d; "
+                            "was group %d" % (name, gid,  ogid))
+            self.groupdict[name] = gid
+        return gid
+    def closegroup(self, gid, p):
+        self.groupwidths[gid] = p.getwidth()
+    def checkgroup(self, gid):
+        return gid < self.groups and self.groupwidths[gid] is not None
+
+    def checklookbehindgroup(self, gid, source):
+        if self.lookbehindgroups is not None:
+            if not self.checkgroup(gid):
+                raise source.error('cannot refer to an open group')
+            if gid >= self.lookbehindgroups:
+                raise source.error('cannot refer to group defined in the same '
+                                   'lookbehind subpattern')
+
+class SubPattern:
+    # a subpattern, in intermediate form
+    def __init__(self, state, data=None):
+        self.state = state
+        if data is None:
+            data = []
+        self.data = data
+        self.width = None
+
+    def dump(self, level=0):
+        seqtypes = (tuple, list)
+        for op, av in self.data:
+            print(level*"  " + str(op), end='')
+            if op is IN:
+                # member sublanguage
+                print()
+                for op, a in av:
+                    print((level+1)*"  " + str(op), a)
+            elif op is BRANCH:
+                print()
+                for i, a in enumerate(av[1]):
+                    if i:
+                        print(level*"  " + "OR")
+                    a.dump(level+1)
+            elif op is GROUPREF_EXISTS:
+                condgroup, item_yes, item_no = av
+                print('', condgroup)
+                item_yes.dump(level+1)
+                if item_no:
+                    print(level*"  " + "ELSE")
+                    item_no.dump(level+1)
+            elif isinstance(av, SubPattern):
+                print()
+                av.dump(level+1)
+            elif isinstance(av, seqtypes):
+                nl = False
+                for a in av:
+                    if isinstance(a, SubPattern):
+                        if not nl:
+                            print()
+                        a.dump(level+1)
+                        nl = True
+                    else:
+                        if not nl:
+                            print(' ', end='')
+                        print(a, end='')
+                        nl = False
+                if not nl:
+                    print()
+            else:
+                print('', av)
+    def __repr__(self):
+        return repr(self.data)
+    def __len__(self):
+        return len(self.data)
+    def __delitem__(self, index):
+        del self.data[index]
+    def __getitem__(self, index):
+        if isinstance(index, slice):
+            return SubPattern(self.state, self.data[index])
+        return self.data[index]
+    def __setitem__(self, index, code):
+        self.data[index] = code
+    def insert(self, index, code):
+        self.data.insert(index, code)
+    def append(self, code):
+        self.data.append(code)
+    def getwidth(self):
+        # determine the width (min, max) for this subpattern
+        if self.width is not None:
+            return self.width
+        lo = hi = 0
+        for op, av in self.data:
+            if op is BRANCH:
+                i = MAXREPEAT - 1
+                j = 0
+                for av in av[1]:
+                    l, h = av.getwidth()
+                    i = min(i, l)
+                    j = max(j, h)
+                lo = lo + i
+                hi = hi + j
+            elif op is ATOMIC_GROUP:
+                i, j = av.getwidth()
+                lo = lo + i
+                hi = hi + j
+            elif op is SUBPATTERN:
+                i, j = av[-1].getwidth()
+                lo = lo + i
+                hi = hi + j
+            elif op in _REPEATCODES:
+                i, j = av[2].getwidth()
+                lo = lo + i * av[0]
+                hi = hi + j * av[1]
+            elif op in _UNITCODES:
+                lo = lo + 1
+                hi = hi + 1
+            elif op is GROUPREF:
+                i, j = self.state.groupwidths[av]
+                lo = lo + i
+                hi = hi + j
+            elif op is GROUPREF_EXISTS:
+                i, j = av[1].getwidth()
+                if av[2] is not None:
+                    l, h = av[2].getwidth()
+                    i = min(i, l)
+                    j = max(j, h)
+                else:
+                    i = 0
+                lo = lo + i
+                hi = hi + j
+            elif op is SUCCESS:
+                break
+        self.width = min(lo, MAXREPEAT - 1), min(hi, MAXREPEAT)
+        return self.width
+
+class Tokenizer:
+    def __init__(self, string):
+        self.istext = isinstance(string, str)
+        self.string = string
+        if not self.istext:
+            string = str(string, 'latin1')
+        self.decoded_string = string
+        self.index = 0
+        self.next = None
+        self.__next()
+    def __next(self):
+        index = self.index
+        try:
+            char = self.decoded_string[index]
+        except IndexError:
+            self.next = None
+            return
+        if char == "\\":
+            index += 1
+            try:
+                char += self.decoded_string[index]
+            except IndexError:
+                raise error("bad escape (end of pattern)",
+                            self.string, len(self.string) - 1) from None
+        self.index = index + 1
+        self.next = char
+    def match(self, char):
+        if char == self.next:
+            self.__next()
+            return True
+        return False
+    def get(self):
+        this = self.next
+        self.__next()
+        return this
+    def getwhile(self, n, charset):
+        result = ''
+        for _ in range(n):
+            c = self.next
+            if c not in charset:
+                break
+            result += c
+            self.__next()
+        return result
+    def getuntil(self, terminator, name):
+        result = ''
+        while True:
+            c = self.next
+            self.__next()
+            if c is None:
+                if not result:
+                    raise self.error("missing " + name)
+                raise self.error("missing %s, unterminated name" % terminator,
+                                 len(result))
+            if c == terminator:
+                if not result:
+                    raise self.error("missing " + name, 1)
+                break
+            result += c
+        return result
+    @property
+    def pos(self):
+        return self.index - len(self.next or '')
+    def tell(self):
+        return self.index - len(self.next or '')
+    def seek(self, index):
+        self.index = index
+        self.__next()
+
+    def error(self, msg, offset=0):
+        if not self.istext:
+            msg = msg.encode('ascii', 'backslashreplace').decode('ascii')
+        return error(msg, self.string, self.tell() - offset)
+
+    def checkgroupname(self, name, offset, nested):
+        if not name.isidentifier():
+            msg = "bad character in group name %r" % name
+            raise self.error(msg, len(name) + offset)
+        if not (self.istext or name.isascii()):
+            import warnings
+            warnings.warn(
+                "bad character in group name %a at position %d" %
+                (name, self.tell() - len(name) - offset),
+                DeprecationWarning, stacklevel=nested + 7
+            )
+
+def _class_escape(source, escape):
+    # handle escape code inside character class
+    code = ESCAPES.get(escape)
+    if code:
+        return code
+    code = CATEGORIES.get(escape)
+    if code and code[0] is IN:
+        return code
+    try:
+        c = escape[1:2]
+        if c == "x":
+            # hexadecimal escape (exactly two digits)
+            escape += source.getwhile(2, HEXDIGITS)
+            if len(escape) != 4:
+                raise source.error("incomplete escape %s" % escape, len(escape))
+            return LITERAL, int(escape[2:], 16)
+        elif c == "u" and source.istext:
+            # unicode escape (exactly four digits)
+            escape += source.getwhile(4, HEXDIGITS)
+            if len(escape) != 6:
+                raise source.error("incomplete escape %s" % escape, len(escape))
+            return LITERAL, int(escape[2:], 16)
+        elif c == "U" and source.istext:
+            # unicode escape (exactly eight digits)
+            escape += source.getwhile(8, HEXDIGITS)
+            if len(escape) != 10:
+                raise source.error("incomplete escape %s" % escape, len(escape))
+            c = int(escape[2:], 16)
+            chr(c) # raise ValueError for invalid code
+            return LITERAL, c
+        elif c == "N" and source.istext:
+            import unicodedata
+            # named unicode escape e.g. \N{EM DASH}
+            if not source.match('{'):
+                raise source.error("missing {")
+            charname = source.getuntil('}', 'character name')
+            try:
+                c = ord(unicodedata.lookup(charname))
+            except (KeyError, TypeError):
+                raise source.error("undefined character name %r" % charname,
+                                   len(charname) + len(r'\N{}')) from None
+            return LITERAL, c
+        elif c in OCTDIGITS:
+            # octal escape (up to three digits)
+            escape += source.getwhile(2, OCTDIGITS)
+            c = int(escape[1:], 8)
+            if c > 0o377:
+                raise source.error('octal escape value %s outside of '
+                                   'range 0-0o377' % escape, len(escape))
+            return LITERAL, c
+        elif c in DIGITS:
+            raise ValueError
+        if len(escape) == 2:
+            if c in ASCIILETTERS:
+                raise source.error('bad escape %s' % escape, len(escape))
+            return LITERAL, ord(escape[1])
+    except ValueError:
+        pass
+    raise source.error("bad escape %s" % escape, len(escape))
+
+def _escape(source, escape, state):
+    # handle escape code in expression
+    code = CATEGORIES.get(escape)
+    if code:
+        return code
+    code = ESCAPES.get(escape)
+    if code:
+        return code
+    try:
+        c = escape[1:2]
+        if c == "x":
+            # hexadecimal escape
+            escape += source.getwhile(2, HEXDIGITS)
+            if len(escape) != 4:
+                raise source.error("incomplete escape %s" % escape, len(escape))
+            return LITERAL, int(escape[2:], 16)
+        elif c == "u" and source.istext:
+            # unicode escape (exactly four digits)
+            escape += source.getwhile(4, HEXDIGITS)
+            if len(escape) != 6:
+                raise source.error("incomplete escape %s" % escape, len(escape))
+            return LITERAL, int(escape[2:], 16)
+        elif c == "U" and source.istext:
+            # unicode escape (exactly eight digits)
+            escape += source.getwhile(8, HEXDIGITS)
+            if len(escape) != 10:
+                raise source.error("incomplete escape %s" % escape, len(escape))
+            c = int(escape[2:], 16)
+            chr(c) # raise ValueError for invalid code
+            return LITERAL, c
+        elif c == "N" and source.istext:
+            import unicodedata
+            # named unicode escape e.g. \N{EM DASH}
+            if not source.match('{'):
+                raise source.error("missing {")
+            charname = source.getuntil('}', 'character name')
+            try:
+                c = ord(unicodedata.lookup(charname))
+            except (KeyError, TypeError):
+                raise source.error("undefined character name %r" % charname,
+                                   len(charname) + len(r'\N{}')) from None
+            return LITERAL, c
+        elif c == "0":
+            # octal escape
+            escape += source.getwhile(2, OCTDIGITS)
+            return LITERAL, int(escape[1:], 8)
+        elif c in DIGITS:
+            # octal escape *or* decimal group reference (sigh)
+            if source.next in DIGITS:
+                escape += source.get()
+                if (escape[1] in OCTDIGITS and escape[2] in OCTDIGITS and
+                    source.next in OCTDIGITS):
+                    # got three octal digits; this is an octal escape
+                    escape += source.get()
+                    c = int(escape[1:], 8)
+                    if c > 0o377:
+                        raise source.error('octal escape value %s outside of '
+                                           'range 0-0o377' % escape,
+                                           len(escape))
+                    return LITERAL, c
+            # not an octal escape, so this is a group reference
+            group = int(escape[1:])
+            if group < state.groups:
+                if not state.checkgroup(group):
+                    raise source.error("cannot refer to an open group",
+                                       len(escape))
+                state.checklookbehindgroup(group, source)
+                return GROUPREF, group
+            raise source.error("invalid group reference %d" % group, len(escape) - 1)
+        if len(escape) == 2:
+            if c in ASCIILETTERS:
+                raise source.error("bad escape %s" % escape, len(escape))
+            return LITERAL, ord(escape[1])
+    except ValueError:
+        pass
+    raise source.error("bad escape %s" % escape, len(escape))
+
+def _uniq(items):
+    return list(dict.fromkeys(items))
+
+def _parse_sub(source, state, verbose, nested):
+    # parse an alternation: a|b|c
+
+    items = []
+    itemsappend = items.append
+    sourcematch = source.match
+    start = source.tell()
+    while True:
+        itemsappend(_parse(source, state, verbose, nested + 1,
+                           not nested and not items))
+        if not sourcematch("|"):
+            break
+        if not nested:
+            verbose = state.flags & SRE_FLAG_VERBOSE
+
+    if len(items) == 1:
+        return items[0]
+
+    subpattern = SubPattern(state)
+
+    # check if all items share a common prefix
+    while True:
+        prefix = None
+        for item in items:
+            if not item:
+                break
+            if prefix is None:
+                prefix = item[0]
+            elif item[0] != prefix:
+                break
+        else:
+            # all subitems start with a common "prefix".
+            # move it out of the branch
+            for item in items:
+                del item[0]
+            subpattern.append(prefix)
+            continue # check next one
+        break
+
+    # check if the branch can be replaced by a character set
+    set = []
+    for item in items:
+        if len(item) != 1:
+            break
+        op, av = item[0]
+        if op is LITERAL:
+            set.append((op, av))
+        elif op is IN and av[0][0] is not NEGATE:
+            set.extend(av)
+        else:
+            break
+    else:
+        # we can store this as a character set instead of a
+        # branch (the compiler may optimize this even more)
+        subpattern.append((IN, _uniq(set)))
+        return subpattern
+
+    subpattern.append((BRANCH, (None, items)))
+    return subpattern
+
+def _parse(source, state, verbose, nested, first=False):
+    # parse a simple pattern
+    subpattern = SubPattern(state)
+
+    # precompute constants into local variables
+    subpatternappend = subpattern.append
+    sourceget = source.get
+    sourcematch = source.match
+    _len = len
+    _ord = ord
+
+    while True:
+
+        this = source.next
+        if this is None:
+            break # end of pattern
+        if this in "|)":
+            break # end of subpattern
+        sourceget()
+
+        if verbose:
+            # skip whitespace and comments
+            if this in WHITESPACE:
+                continue
+            if this == "#":
+                while True:
+                    this = sourceget()
+                    if this is None or this == "\n":
+                        break
+                continue
+
+        if this[0] == "\\":
+            code = _escape(source, this, state)
+            subpatternappend(code)
+
+        elif this not in SPECIAL_CHARS:
+            subpatternappend((LITERAL, _ord(this)))
+
+        elif this == "[":
+            here = source.tell() - 1
+            # character set
+            set = []
+            setappend = set.append
+##          if sourcematch(":"):
+##              pass # handle character classes
+            if source.next == '[':
+                import warnings
+                warnings.warn(
+                    'Possible nested set at position %d' % source.tell(),
+                    FutureWarning, stacklevel=nested + 6
+                )
+            negate = sourcematch("^")
+            # check remaining characters
+            while True:
+                this = sourceget()
+                if this is None:
+                    raise source.error("unterminated character set",
+                                       source.tell() - here)
+                if this == "]" and set:
+                    break
+                elif this[0] == "\\":
+                    code1 = _class_escape(source, this)
+                else:
+                    if set and this in '-&~|' and source.next == this:
+                        import warnings
+                        warnings.warn(
+                            'Possible set %s at position %d' % (
+                                'difference' if this == '-' else
+                                'intersection' if this == '&' else
+                                'symmetric difference' if this == '~' else
+                                'union',
+                                source.tell() - 1),
+                            FutureWarning, stacklevel=nested + 6
+                        )
+                    code1 = LITERAL, _ord(this)
+                if sourcematch("-"):
+                    # potential range
+                    that = sourceget()
+                    if that is None:
+                        raise source.error("unterminated character set",
+                                           source.tell() - here)
+                    if that == "]":
+                        if code1[0] is IN:
+                            code1 = code1[1][0]
+                        setappend(code1)
+                        setappend((LITERAL, _ord("-")))
+                        break
+                    if that[0] == "\\":
+                        code2 = _class_escape(source, that)
+                    else:
+                        if that == '-':
+                            import warnings
+                            warnings.warn(
+                                'Possible set difference at position %d' % (
+                                    source.tell() - 2),
+                                FutureWarning, stacklevel=nested + 6
+                            )
+                        code2 = LITERAL, _ord(that)
+                    if code1[0] != LITERAL or code2[0] != LITERAL:
+                        msg = "bad character range %s-%s" % (this, that)
+                        raise source.error(msg, len(this) + 1 + len(that))
+                    lo = code1[1]
+                    hi = code2[1]
+                    if hi < lo:
+                        msg = "bad character range %s-%s" % (this, that)
+                        raise source.error(msg, len(this) + 1 + len(that))
+                    setappend((RANGE, (lo, hi)))
+                else:
+                    if code1[0] is IN:
+                        code1 = code1[1][0]
+                    setappend(code1)
+
+            set = _uniq(set)
+            # XXX: <fl> should move set optimization to compiler!
+            if _len(set) == 1 and set[0][0] is LITERAL:
+                # optimization
+                if negate:
+                    subpatternappend((NOT_LITERAL, set[0][1]))
+                else:
+                    subpatternappend(set[0])
+            else:
+                if negate:
+                    set.insert(0, (NEGATE, None))
+                # charmap optimization can't be added here because
+                # global flags still are not known
+                subpatternappend((IN, set))
+
+        elif this in REPEAT_CHARS:
+            # repeat previous item
+            here = source.tell()
+            if this == "?":
+                min, max = 0, 1
+            elif this == "*":
+                min, max = 0, MAXREPEAT
+
+            elif this == "+":
+                min, max = 1, MAXREPEAT
+            elif this == "{":
+                if source.next == "}":
+                    subpatternappend((LITERAL, _ord(this)))
+                    continue
+
+                min, max = 0, MAXREPEAT
+                lo = hi = ""
+                while source.next in DIGITS:
+                    lo += sourceget()
+                if sourcematch(","):
+                    while source.next in DIGITS:
+                        hi += sourceget()
+                else:
+                    hi = lo
+                if not sourcematch("}"):
+                    subpatternappend((LITERAL, _ord(this)))
+                    source.seek(here)
+                    continue
+
+                if lo:
+                    min = int(lo)
+                    if min >= MAXREPEAT:
+                        raise OverflowError("the repetition number is too large")
+                if hi:
+                    max = int(hi)
+                    if max >= MAXREPEAT:
+                        raise OverflowError("the repetition number is too large")
+                    if max < min:
+                        raise source.error("min repeat greater than max repeat",
+                                           source.tell() - here)
+            else:
+                raise AssertionError("unsupported quantifier %r" % (char,))
+            # figure out which item to repeat
+            if subpattern:
+                item = subpattern[-1:]
+            else:
+                item = None
+            if not item or item[0][0] is AT:
+                raise source.error("nothing to repeat",
+                                   source.tell() - here + len(this))
+            if item[0][0] in _REPEATCODES:
+                raise source.error("multiple repeat",
+                                   source.tell() - here + len(this))
+            if item[0][0] is SUBPATTERN:
+                group, add_flags, del_flags, p = item[0][1]
+                if group is None and not add_flags and not del_flags:
+                    item = p
+            if sourcematch("?"):
+                # Non-Greedy Match
+                subpattern[-1] = (MIN_REPEAT, (min, max, item))
+            elif sourcematch("+"):
+                # Possessive Match (Always Greedy)
+                subpattern[-1] = (POSSESSIVE_REPEAT, (min, max, item))
+            else:
+                # Greedy Match
+                subpattern[-1] = (MAX_REPEAT, (min, max, item))
+
+        elif this == ".":
+            subpatternappend((ANY, None))
+
+        elif this == "(":
+            start = source.tell() - 1
+            capture = True
+            atomic = False
+            name = None
+            add_flags = 0
+            del_flags = 0
+            if sourcematch("?"):
+                # options
+                char = sourceget()
+                if char is None:
+                    raise source.error("unexpected end of pattern")
+                if char == "P":
+                    # python extensions
+                    if sourcematch("<"):
+                        # named group: skip forward to end of name
+                        name = source.getuntil(">", "group name")
+                        source.checkgroupname(name, 1, nested)
+                    elif sourcematch("="):
+                        # named backreference
+                        name = source.getuntil(")", "group name")
+                        source.checkgroupname(name, 1, nested)
+                        gid = state.groupdict.get(name)
+                        if gid is None:
+                            msg = "unknown group name %r" % name
+                            raise source.error(msg, len(name) + 1)
+                        if not state.checkgroup(gid):
+                            raise source.error("cannot refer to an open group",
+                                               len(name) + 1)
+                        state.checklookbehindgroup(gid, source)
+                        subpatternappend((GROUPREF, gid))
+                        continue
+
+                    else:
+                        char = sourceget()
+                        if char is None:
+                            raise source.error("unexpected end of pattern")
+                        raise source.error("unknown extension ?P" + char,
+                                           len(char) + 2)
+                elif char == ":":
+                    # non-capturing group
+                    capture = False
+                elif char == "#":
+                    # comment
+                    while True:
+                        if source.next is None:
+                            raise source.error("missing ), unterminated comment",
+                                               source.tell() - start)
+                        if sourceget() == ")":
+                            break
+                    continue
+
+                elif char in "=!<":
+                    # lookahead assertions
+                    dir = 1
+                    if char == "<":
+                        char = sourceget()
+                        if char is None:
+                            raise source.error("unexpected end of pattern")
+                        if char not in "=!":
+                            raise source.error("unknown extension ?<" + char,
+                                               len(char) + 2)
+                        dir = -1 # lookbehind
+                        lookbehindgroups = state.lookbehindgroups
+                        if lookbehindgroups is None:
+                            state.lookbehindgroups = state.groups
+                    p = _parse_sub(source, state, verbose, nested + 1)
+                    if dir < 0:
+                        if lookbehindgroups is None:
+                            state.lookbehindgroups = None
+                    if not sourcematch(")"):
+                        raise source.error("missing ), unterminated subpattern",
+                                           source.tell() - start)
+                    if char == "=":
+                        subpatternappend((ASSERT, (dir, p)))
+                    else:
+                        subpatternappend((ASSERT_NOT, (dir, p)))
+                    continue
+
+                elif char == "(":
+                    # conditional backreference group
+                    condname = source.getuntil(")", "group name")
+                    if condname.isidentifier():
+                        source.checkgroupname(condname, 1, nested)
+                        condgroup = state.groupdict.get(condname)
+                        if condgroup is None:
+                            msg = "unknown group name %r" % condname
+                            raise source.error(msg, len(condname) + 1)
+                    else:
+                        try:
+                            condgroup = int(condname)
+                            if condgroup < 0:
+                                raise ValueError
+                        except ValueError:
+                            msg = "bad character in group name %r" % condname
+                            raise source.error(msg, len(condname) + 1) from None
+                        if not condgroup:
+                            raise source.error("bad group number",
+                                               len(condname) + 1)
+                        if condgroup >= MAXGROUPS:
+                            msg = "invalid group reference %d" % condgroup
+                            raise source.error(msg, len(condname) + 1)
+                        if condgroup not in state.grouprefpos:
+                            state.grouprefpos[condgroup] = (
+                                source.tell() - len(condname) - 1
+                            )
+                        if not (condname.isdecimal() and condname.isascii()):
+                            import warnings
+                            warnings.warn(
+                                "bad character in group name %s at position %d" %
+                                (repr(condname) if source.istext else ascii(condname),
+                                 source.tell() - len(condname) - 1),
+                                DeprecationWarning, stacklevel=nested + 6
+                            )
+                    state.checklookbehindgroup(condgroup, source)
+                    item_yes = _parse(source, state, verbose, nested + 1)
+                    if source.match("|"):
+                        item_no = _parse(source, state, verbose, nested + 1)
+                        if source.next == "|":
+                            raise source.error("conditional backref with more than two branches")
+                    else:
+                        item_no = None
+                    if not source.match(")"):
+                        raise source.error("missing ), unterminated subpattern",
+                                           source.tell() - start)
+                    subpatternappend((GROUPREF_EXISTS, (condgroup, item_yes, item_no)))
+                    continue
+
+                elif char == ">":
+                    # non-capturing, atomic group
+                    capture = False
+                    atomic = True
+                elif char in FLAGS or char == "-":
+                    # flags
+                    flags = _parse_flags(source, state, char)
+                    if flags is None:  # global flags
+                        if not first or subpattern:
+                            raise source.error('global flags not at the start '
+                                               'of the expression',
+                                               source.tell() - start)
+                        verbose = state.flags & SRE_FLAG_VERBOSE
+                        continue
+
+                    add_flags, del_flags = flags
+                    capture = False
+                else:
+                    raise source.error("unknown extension ?" + char,
+                                       len(char) + 1)
+
+            # parse group contents
+            if capture:
+                try:
+                    group = state.opengroup(name)
+                except error as err:
+                    raise source.error(err.msg, len(name) + 1) from None
+            else:
+                group = None
+            sub_verbose = ((verbose or (add_flags & SRE_FLAG_VERBOSE)) and
+                           not (del_flags & SRE_FLAG_VERBOSE))
+            p = _parse_sub(source, state, sub_verbose, nested + 1)
+            if not source.match(")"):
+                raise source.error("missing ), unterminated subpattern",
+                                   source.tell() - start)
+            if group is not None:
+                state.closegroup(group, p)
+            if atomic:
+                assert group is None
+                subpatternappend((ATOMIC_GROUP, p))
+            else:
+                subpatternappend((SUBPATTERN, (group, add_flags, del_flags, p)))
+
+        elif this == "^":
+            subpatternappend((AT, AT_BEGINNING))
+
+        elif this == "$":
+            subpatternappend((AT, AT_END))
+
+        else:
+            raise AssertionError("unsupported special character %r" % (char,))
+
+    # unpack non-capturing groups
+    for i in range(len(subpattern))[::-1]:
+        op, av = subpattern[i]
+        if op is SUBPATTERN:
+            group, add_flags, del_flags, p = av
+            if group is None and not add_flags and not del_flags:
+                subpattern[i: i+1] = p
+
+    return subpattern
+
+def _parse_flags(source, state, char):
+    sourceget = source.get
+    add_flags = 0
+    del_flags = 0
+    if char != "-":
+        while True:
+            flag = FLAGS[char]
+            if source.istext:
+                if char == 'L':
+                    msg = "bad inline flags: cannot use 'L' flag with a str pattern"
+                    raise source.error(msg)
+            else:
+                if char == 'u':
+                    msg = "bad inline flags: cannot use 'u' flag with a bytes pattern"
+                    raise source.error(msg)
+            add_flags |= flag
+            if (flag & TYPE_FLAGS) and (add_flags & TYPE_FLAGS) != flag:
+                msg = "bad inline flags: flags 'a', 'u' and 'L' are incompatible"
+                raise source.error(msg)
+            char = sourceget()
+            if char is None:
+                raise source.error("missing -, : or )")
+            if char in ")-:":
+                break
+            if char not in FLAGS:
+                msg = "unknown flag" if char.isalpha() else "missing -, : or )"
+                raise source.error(msg, len(char))
+    if char == ")":
+        state.flags |= add_flags
+        return None
+    if add_flags & GLOBAL_FLAGS:
+        raise source.error("bad inline flags: cannot turn on global flag", 1)
+    if char == "-":
+        char = sourceget()
+        if char is None:
+            raise source.error("missing flag")
+        if char not in FLAGS:
+            msg = "unknown flag" if char.isalpha() else "missing flag"
+            raise source.error(msg, len(char))
+        while True:
+            flag = FLAGS[char]
+            if flag & TYPE_FLAGS:
+                msg = "bad inline flags: cannot turn off flags 'a', 'u' and 'L'"
+                raise source.error(msg)
+            del_flags |= flag
+            char = sourceget()
+            if char is None:
+                raise source.error("missing :")
+            if char == ":":
+                break
+            if char not in FLAGS:
+                msg = "unknown flag" if char.isalpha() else "missing :"
+                raise source.error(msg, len(char))
+    assert char == ":"
+    if del_flags & GLOBAL_FLAGS:
+        raise source.error("bad inline flags: cannot turn off global flag", 1)
+    if add_flags & del_flags:
+        raise source.error("bad inline flags: flag turned on and off", 1)
+    return add_flags, del_flags
+
+def fix_flags(src, flags):
+    # Check and fix flags according to the type of pattern (str or bytes)
+    if isinstance(src, str):
+        if flags & SRE_FLAG_LOCALE:
+            raise ValueError("cannot use LOCALE flag with a str pattern")
+        if not flags & SRE_FLAG_ASCII:
+            flags |= SRE_FLAG_UNICODE
+        elif flags & SRE_FLAG_UNICODE:
+            raise ValueError("ASCII and UNICODE flags are incompatible")
+    else:
+        if flags & SRE_FLAG_UNICODE:
+            raise ValueError("cannot use UNICODE flag with a bytes pattern")
+        if flags & SRE_FLAG_LOCALE and flags & SRE_FLAG_ASCII:
+            raise ValueError("ASCII and LOCALE flags are incompatible")
+    return flags
+
+def parse(str, flags=0, state=None):
+    # parse 're' pattern into list of (opcode, argument) tuples
+
+    source = Tokenizer(str)
+
+    if state is None:
+        state = State()
+    state.flags = flags
+    state.str = str
+
+    p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0)
+    p.state.flags = fix_flags(str, p.state.flags)
+
+    if source.next is not None:
+        assert source.next == ")"
+        raise source.error("unbalanced parenthesis")
+
+    for g in p.state.grouprefpos:
+        if g >= p.state.groups:
+            msg = "invalid group reference %d" % g
+            raise error(msg, str, p.state.grouprefpos[g])
+
+    if flags & SRE_FLAG_DEBUG:
+        p.dump()
+
+    return p
+
+def parse_template(source, state):
+    # parse 're' replacement string into list of literals and
+    # group references
+    s = Tokenizer(source)
+    sget = s.get
+    groups = []
+    literals = []
+    literal = []
+    lappend = literal.append
+    def addgroup(index, pos):
+        if index > state.groups:
+            raise s.error("invalid group reference %d" % index, pos)
+        if literal:
+            literals.append(''.join(literal))
+            del literal[:]
+        groups.append((len(literals), index))
+        literals.append(None)
+    groupindex = state.groupindex
+    while True:
+        this = sget()
+        if this is None:
+            break # end of replacement string
+        if this[0] == "\\":
+            # group
+            c = this[1]
+            if c == "g":
+                if not s.match("<"):
+                    raise s.error("missing <")
+                name = s.getuntil(">", "group name")
+                if name.isidentifier():
+                    s.checkgroupname(name, 1, -1)
+                    try:
+                        index = groupindex[name]
+                    except KeyError:
+                        raise IndexError("unknown group name %r" % name) from None
+                else:
+                    try:
+                        index = int(name)
+                        if index < 0:
+                            raise ValueError
+                    except ValueError:
+                        raise s.error("bad character in group name %r" % name,
+                                      len(name) + 1) from None
+                    if index >= MAXGROUPS:
+                        raise s.error("invalid group reference %d" % index,
+                                      len(name) + 1)
+                    if not (name.isdecimal() and name.isascii()):
+                        import warnings
+                        warnings.warn(
+                            "bad character in group name %s at position %d" %
+                            (repr(name) if s.istext else ascii(name),
+                             s.tell() - len(name) - 1),
+                            DeprecationWarning, stacklevel=5
+                        )
+                addgroup(index, len(name) + 1)
+            elif c == "0":
+                if s.next in OCTDIGITS:
+                    this += sget()
+                    if s.next in OCTDIGITS:
+                        this += sget()
+                lappend(chr(int(this[1:], 8) & 0xff))
+            elif c in DIGITS:
+                isoctal = False
+                if s.next in DIGITS:
+                    this += sget()
+                    if (c in OCTDIGITS and this[2] in OCTDIGITS and
+                        s.next in OCTDIGITS):
+                        this += sget()
+                        isoctal = True
+                        c = int(this[1:], 8)
+                        if c > 0o377:
+                            raise s.error('octal escape value %s outside of '
+                                          'range 0-0o377' % this, len(this))
+                        lappend(chr(c))
+                if not isoctal:
+                    addgroup(int(this[1:]), len(this) - 1)
+            else:
+                try:
+                    this = chr(ESCAPES[this][1])
+                except KeyError:
+                    if c in ASCIILETTERS:
+                        raise s.error('bad escape %s' % this, len(this)) from None
+                lappend(this)
+        else:
+            lappend(this)
+    if literal:
+        literals.append(''.join(literal))
+    if not isinstance(source, str):
+        # The tokenizer implicitly decodes bytes objects as latin-1, we must
+        # therefore re-encode the final representation.
+        literals = [None if s is None else s.encode('latin-1') for s in literals]
+    return groups, literals
+
+def expand_template(template, match):
+    g = match.group
+    empty = match.string[:0]
+    groups, literals = template
+    literals = literals[:]
+    try:
+        for index, group in groups:
+            literals[index] = g(group) or empty
+    except IndexError:
+        raise error("invalid group reference %d" % index) from None
+    return empty.join(literals)