intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

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diff --git a/contrib/python/ipython/py2/IPython/core/ultratb.py b/contrib/python/ipython/py2/IPython/core/ultratb.py
new file mode 100644
index 0000000000..a855145825
--- /dev/null
+++ b/contrib/python/ipython/py2/IPython/core/ultratb.py
@@ -0,0 +1,1499 @@
+# -*- coding: utf-8 -*-
+"""
+Verbose and colourful traceback formatting.
+
+**ColorTB**
+
+I've always found it a bit hard to visually parse tracebacks in Python.  The
+ColorTB class is a solution to that problem.  It colors the different parts of a
+traceback in a manner similar to what you would expect from a syntax-highlighting
+text editor.
+
+Installation instructions for ColorTB::
+
+    import sys,ultratb
+    sys.excepthook = ultratb.ColorTB()
+
+**VerboseTB**
+
+I've also included a port of Ka-Ping Yee's "cgitb.py" that produces all kinds
+of useful info when a traceback occurs.  Ping originally had it spit out HTML
+and intended it for CGI programmers, but why should they have all the fun?  I
+altered it to spit out colored text to the terminal.  It's a bit overwhelming,
+but kind of neat, and maybe useful for long-running programs that you believe
+are bug-free.  If a crash *does* occur in that type of program you want details.
+Give it a shot--you'll love it or you'll hate it.
+
+.. note::
+
+  The Verbose mode prints the variables currently visible where the exception
+  happened (shortening their strings if too long). This can potentially be
+  very slow, if you happen to have a huge data structure whose string
+  representation is complex to compute. Your computer may appear to freeze for
+  a while with cpu usage at 100%. If this occurs, you can cancel the traceback
+  with Ctrl-C (maybe hitting it more than once).
+
+  If you encounter this kind of situation often, you may want to use the
+  Verbose_novars mode instead of the regular Verbose, which avoids formatting
+  variables (but otherwise includes the information and context given by
+  Verbose).
+
+.. note::
+
+  The verbose mode print all variables in the stack, which means it can
+  potentially leak sensitive information like access keys, or unencryted
+  password.
+
+Installation instructions for VerboseTB::
+
+    import sys,ultratb
+    sys.excepthook = ultratb.VerboseTB()
+
+Note:  Much of the code in this module was lifted verbatim from the standard
+library module 'traceback.py' and Ka-Ping Yee's 'cgitb.py'.
+
+Color schemes
+-------------
+
+The colors are defined in the class TBTools through the use of the
+ColorSchemeTable class. Currently the following exist:
+
+  - NoColor: allows all of this module to be used in any terminal (the color
+    escapes are just dummy blank strings).
+
+  - Linux: is meant to look good in a terminal like the Linux console (black
+    or very dark background).
+
+  - LightBG: similar to Linux but swaps dark/light colors to be more readable
+    in light background terminals.
+
+  - Neutral: a neutral color scheme that should be readable on both light and
+    dark background
+
+You can implement other color schemes easily, the syntax is fairly
+self-explanatory. Please send back new schemes you develop to the author for
+possible inclusion in future releases.
+
+Inheritance diagram:
+
+.. inheritance-diagram:: IPython.core.ultratb
+   :parts: 3
+"""
+
+#*****************************************************************************
+# Copyright (C) 2001 Nathaniel Gray <n8gray@caltech.edu>
+# Copyright (C) 2001-2004 Fernando Perez <fperez@colorado.edu>
+#
+# Distributed under the terms of the BSD License.  The full license is in
+# the file COPYING, distributed as part of this software.
+#*****************************************************************************
+
+from __future__ import absolute_import
+from __future__ import unicode_literals
+from __future__ import print_function
+
+import dis
+import inspect
+import keyword
+import linecache
+import os
+import pydoc
+import re
+import sys
+import time
+import tokenize
+import traceback
+import types
+
+try:  # Python 2
+    generate_tokens = tokenize.generate_tokens
+except AttributeError:  # Python 3
+    generate_tokens = tokenize.tokenize
+
+# For purposes of monkeypatching inspect to fix a bug in it.
+from inspect import getsourcefile, getfile, getmodule, \
+    ismodule, isclass, ismethod, isfunction, istraceback, isframe, iscode
+
+# IPython's own modules
+from IPython import get_ipython
+from IPython.core import debugger
+from IPython.core.display_trap import DisplayTrap
+from IPython.core.excolors import exception_colors
+from IPython.utils import PyColorize
+from IPython.utils import openpy
+from IPython.utils import path as util_path
+from IPython.utils import py3compat
+from IPython.utils import ulinecache
+from IPython.utils.data import uniq_stable
+from IPython.utils.terminal import get_terminal_size
+from logging import info, error
+
+import IPython.utils.colorable as colorable
+
+# Globals
+# amount of space to put line numbers before verbose tracebacks
+INDENT_SIZE = 8
+
+# Default color scheme.  This is used, for example, by the traceback
+# formatter.  When running in an actual IPython instance, the user's rc.colors
+# value is used, but having a module global makes this functionality available
+# to users of ultratb who are NOT running inside ipython.
+DEFAULT_SCHEME = 'NoColor'
+
+# ---------------------------------------------------------------------------
+# Code begins
+
+# Utility functions
+def inspect_error():
+    """Print a message about internal inspect errors.
+
+    These are unfortunately quite common."""
+
+    error('Internal Python error in the inspect module.\n'
+          'Below is the traceback from this internal error.\n')
+
+
+# This function is a monkeypatch we apply to the Python inspect module. We have
+# now found when it's needed (see discussion on issue gh-1456), and we have a
+# test case (IPython.core.tests.test_ultratb.ChangedPyFileTest) that fails if
+# the monkeypatch is not applied. TK, Aug 2012.
+def findsource(object):
+    """Return the entire source file and starting line number for an object.
+
+    The argument may be a module, class, method, function, traceback, frame,
+    or code object.  The source code is returned as a list of all the lines
+    in the file and the line number indexes a line in that list.  An IOError
+    is raised if the source code cannot be retrieved.
+
+    FIXED version with which we monkeypatch the stdlib to work around a bug."""
+
+    file = getsourcefile(object) or getfile(object)
+    # If the object is a frame, then trying to get the globals dict from its
+    # module won't work. Instead, the frame object itself has the globals
+    # dictionary.
+    globals_dict = None
+    if inspect.isframe(object):
+        # XXX: can this ever be false?
+        globals_dict = object.f_globals
+    else:
+        module = getmodule(object, file)
+        if module:
+            globals_dict = module.__dict__
+    lines = linecache.getlines(file, globals_dict)
+    if not lines:
+        raise IOError('could not get source code')
+
+    if ismodule(object):
+        return lines, 0
+
+    if isclass(object):
+        name = object.__name__
+        pat = re.compile(r'^(\s*)class\s*' + name + r'\b')
+        # make some effort to find the best matching class definition:
+        # use the one with the least indentation, which is the one
+        # that's most probably not inside a function definition.
+        candidates = []
+        for i in range(len(lines)):
+            match = pat.match(lines[i])
+            if match:
+                # if it's at toplevel, it's already the best one
+                if lines[i][0] == 'c':
+                    return lines, i
+                # else add whitespace to candidate list
+                candidates.append((match.group(1), i))
+        if candidates:
+            # this will sort by whitespace, and by line number,
+            # less whitespace first
+            candidates.sort()
+            return lines, candidates[0][1]
+        else:
+            raise IOError('could not find class definition')
+
+    if ismethod(object):
+        object = object.__func__
+    if isfunction(object):
+        object = object.__code__
+    if istraceback(object):
+        object = object.tb_frame
+    if isframe(object):
+        object = object.f_code
+    if iscode(object):
+        if not hasattr(object, 'co_firstlineno'):
+            raise IOError('could not find function definition')
+        pat = re.compile(r'^(\s*def\s)|(.*(?<!\w)lambda(:|\s))|^(\s*@)')
+        pmatch = pat.match
+        # fperez - fix: sometimes, co_firstlineno can give a number larger than
+        # the length of lines, which causes an error.  Safeguard against that.
+        lnum = min(object.co_firstlineno, len(lines)) - 1
+        while lnum > 0:
+            if pmatch(lines[lnum]):
+                break
+            lnum -= 1
+
+        return lines, lnum
+    raise IOError('could not find code object')
+
+
+# This is a patched version of inspect.getargs that applies the (unmerged)
+# patch for http://bugs.python.org/issue14611 by Stefano Taschini.  This fixes
+# https://github.com/ipython/ipython/issues/8205 and
+# https://github.com/ipython/ipython/issues/8293
+def getargs(co):
+    """Get information about the arguments accepted by a code object.
+
+    Three things are returned: (args, varargs, varkw), where 'args' is
+    a list of argument names (possibly containing nested lists), and
+    'varargs' and 'varkw' are the names of the * and ** arguments or None."""
+    if not iscode(co):
+        raise TypeError('{!r} is not a code object'.format(co))
+
+    nargs = co.co_argcount
+    names = co.co_varnames
+    args = list(names[:nargs])
+    step = 0
+
+    # The following acrobatics are for anonymous (tuple) arguments.
+    for i in range(nargs):
+        if args[i][:1] in ('', '.'):
+            stack, remain, count = [], [], []
+            while step < len(co.co_code):
+                op = ord(co.co_code[step])
+                step = step + 1
+                if op >= dis.HAVE_ARGUMENT:
+                    opname = dis.opname[op]
+                    value = ord(co.co_code[step]) + ord(co.co_code[step+1])*256
+                    step = step + 2
+                    if opname in ('UNPACK_TUPLE', 'UNPACK_SEQUENCE'):
+                        remain.append(value)
+                        count.append(value)
+                    elif opname in ('STORE_FAST', 'STORE_DEREF'):
+                        if op in dis.haslocal:
+                            stack.append(co.co_varnames[value])
+                        elif op in dis.hasfree:
+                            stack.append((co.co_cellvars + co.co_freevars)[value])
+                        # Special case for sublists of length 1: def foo((bar))
+                        # doesn't generate the UNPACK_TUPLE bytecode, so if
+                        # `remain` is empty here, we have such a sublist.
+                        if not remain:
+                            stack[0] = [stack[0]]
+                            break
+                        else:
+                            remain[-1] = remain[-1] - 1
+                            while remain[-1] == 0:
+                                remain.pop()
+                                size = count.pop()
+                                stack[-size:] = [stack[-size:]]
+                                if not remain:
+                                    break
+                                remain[-1] = remain[-1] - 1
+                            if not remain:
+                                break
+            args[i] = stack[0]
+
+    varargs = None
+    if co.co_flags & inspect.CO_VARARGS:
+        varargs = co.co_varnames[nargs]
+        nargs = nargs + 1
+    varkw = None
+    if co.co_flags & inspect.CO_VARKEYWORDS:
+        varkw = co.co_varnames[nargs]
+    return inspect.Arguments(args, varargs, varkw)
+
+
+# Monkeypatch inspect to apply our bugfix.
+def with_patch_inspect(f):
+    """decorator for monkeypatching inspect.findsource"""
+
+    def wrapped(*args, **kwargs):
+        save_findsource = inspect.findsource
+        save_getargs = inspect.getargs
+        inspect.findsource = findsource
+        inspect.getargs = getargs
+        try:
+            return f(*args, **kwargs)
+        finally:
+            inspect.findsource = save_findsource
+            inspect.getargs = save_getargs
+
+    return wrapped
+
+
+if py3compat.PY3:
+    fixed_getargvalues = inspect.getargvalues
+else:
+    # Fixes for https://github.com/ipython/ipython/issues/8293
+    #       and https://github.com/ipython/ipython/issues/8205.
+    # The relevant bug is caused by failure to correctly handle anonymous tuple
+    # unpacking, which only exists in Python 2.
+    fixed_getargvalues = with_patch_inspect(inspect.getargvalues)
+
+
+def fix_frame_records_filenames(records):
+    """Try to fix the filenames in each record from inspect.getinnerframes().
+
+    Particularly, modules loaded from within zip files have useless filenames
+    attached to their code object, and inspect.getinnerframes() just uses it.
+    """
+    fixed_records = []
+    for frame, filename, line_no, func_name, lines, index in records:
+        # Look inside the frame's globals dictionary for __file__,
+        # which should be better. However, keep Cython filenames since
+        # we prefer the source filenames over the compiled .so file.
+        filename = py3compat.cast_unicode_py2(filename, "utf-8")
+        if not filename.endswith(('.pyx', '.pxd', '.pxi')):
+            better_fn = frame.f_globals.get('__file__', None)
+            if isinstance(better_fn, str):
+                # Check the type just in case someone did something weird with
+                # __file__. It might also be None if the error occurred during
+                # import.
+                filename = better_fn
+        fixed_records.append((frame, filename, line_no, func_name, lines, index))
+    return fixed_records
+
+
+@with_patch_inspect
+def _fixed_getinnerframes(etb, context=1, tb_offset=0):
+    LNUM_POS, LINES_POS, INDEX_POS = 2, 4, 5
+
+    records = fix_frame_records_filenames(inspect.getinnerframes(etb, context))
+    # If the error is at the console, don't build any context, since it would
+    # otherwise produce 5 blank lines printed out (there is no file at the
+    # console)
+    rec_check = records[tb_offset:]
+    try:
+        rname = rec_check[0][1]
+        if rname == '<ipython console>' or rname.endswith('<string>'):
+            return rec_check
+    except IndexError:
+        pass
+
+    aux = traceback.extract_tb(etb)
+    assert len(records) == len(aux)
+    for i, (file, lnum, _, _) in zip(range(len(records)), aux):
+        maybeStart = lnum - 1 - context // 2
+        start = max(maybeStart, 0)
+        end = start + context
+        lines = ulinecache.getlines(file)[start:end]
+        buf = list(records[i])
+        buf[LNUM_POS] = lnum
+        buf[INDEX_POS] = lnum - 1 - start
+        buf[LINES_POS] = lines
+        records[i] = tuple(buf)
+    return records[tb_offset:]
+
+# Helper function -- largely belongs to VerboseTB, but we need the same
+# functionality to produce a pseudo verbose TB for SyntaxErrors, so that they
+# can be recognized properly by ipython.el's py-traceback-line-re
+# (SyntaxErrors have to be treated specially because they have no traceback)
+
+_parser = PyColorize.Parser()
+
+
+def _format_traceback_lines(lnum, index, lines, Colors, lvals=None, scheme=None):
+    numbers_width = INDENT_SIZE - 1
+    res = []
+    i = lnum - index
+
+    # This lets us get fully syntax-highlighted tracebacks.
+    if scheme is None:
+        ipinst = get_ipython()
+        if ipinst is not None:
+            scheme = ipinst.colors
+        else:
+            scheme = DEFAULT_SCHEME
+
+    _line_format = _parser.format2
+
+    for line in lines:
+        line = py3compat.cast_unicode(line)
+
+        new_line, err = _line_format(line, 'str', scheme)
+        if not err: line = new_line
+
+        if i == lnum:
+            # This is the line with the error
+            pad = numbers_width - len(str(i))
+            num = '%s%s' % (debugger.make_arrow(pad), str(lnum))
+            line = '%s%s%s %s%s' % (Colors.linenoEm, num,
+                                    Colors.line, line, Colors.Normal)
+        else:
+            num = '%*s' % (numbers_width, i)
+            line = '%s%s%s %s' % (Colors.lineno, num,
+                                  Colors.Normal, line)
+
+        res.append(line)
+        if lvals and i == lnum:
+            res.append(lvals + '\n')
+        i = i + 1
+    return res
+
+def is_recursion_error(etype, value, records):
+    try:
+        # RecursionError is new in Python 3.5
+        recursion_error_type = RecursionError
+    except NameError:
+        recursion_error_type = RuntimeError
+
+    # The default recursion limit is 1000, but some of that will be taken up
+    # by stack frames in IPython itself. >500 frames probably indicates
+    # a recursion error.
+    return (etype is recursion_error_type) \
+           and str("recursion") in str(value).lower() \
+           and len(records) > 500
+
+def find_recursion(etype, value, records):
+    """Identify the repeating stack frames from a RecursionError traceback
+
+    'records' is a list as returned by VerboseTB.get_records()
+
+    Returns (last_unique, repeat_length)
+    """
+    # This involves a bit of guesswork - we want to show enough of the traceback
+    # to indicate where the recursion is occurring. We guess that the innermost
+    # quarter of the traceback (250 frames by default) is repeats, and find the
+    # first frame (from in to out) that looks different.
+    if not is_recursion_error(etype, value, records):
+        return len(records), 0
+
+    # Select filename, lineno, func_name to track frames with
+    records = [r[1:4] for r in records]
+    inner_frames = records[-(len(records)//4):]
+    frames_repeated = set(inner_frames)
+
+    last_seen_at = {}
+    longest_repeat = 0
+    i = len(records)
+    for frame in reversed(records):
+        i -= 1
+        if frame not in frames_repeated:
+            last_unique = i
+            break
+
+        if frame in last_seen_at:
+            distance = last_seen_at[frame] - i
+            longest_repeat = max(longest_repeat, distance)
+
+        last_seen_at[frame] = i
+    else:
+        last_unique = 0 # The whole traceback was recursion
+
+    return last_unique, longest_repeat
+
+#---------------------------------------------------------------------------
+# Module classes
+class TBTools(colorable.Colorable):
+    """Basic tools used by all traceback printer classes."""
+
+    # Number of frames to skip when reporting tracebacks
+    tb_offset = 0
+
+    def __init__(self, color_scheme='NoColor', call_pdb=False, ostream=None, parent=None, config=None):
+        # Whether to call the interactive pdb debugger after printing
+        # tracebacks or not
+        super(TBTools, self).__init__(parent=parent, config=config)
+        self.call_pdb = call_pdb
+
+        # Output stream to write to.  Note that we store the original value in
+        # a private attribute and then make the public ostream a property, so
+        # that we can delay accessing sys.stdout until runtime.  The way
+        # things are written now, the sys.stdout object is dynamically managed
+        # so a reference to it should NEVER be stored statically.  This
+        # property approach confines this detail to a single location, and all
+        # subclasses can simply access self.ostream for writing.
+        self._ostream = ostream
+
+        # Create color table
+        self.color_scheme_table = exception_colors()
+
+        self.set_colors(color_scheme)
+        self.old_scheme = color_scheme  # save initial value for toggles
+
+        if call_pdb:
+            self.pdb = debugger.Pdb()
+        else:
+            self.pdb = None
+
+    def _get_ostream(self):
+        """Output stream that exceptions are written to.
+
+        Valid values are:
+
+        - None: the default, which means that IPython will dynamically resolve
+          to sys.stdout.  This ensures compatibility with most tools, including
+          Windows (where plain stdout doesn't recognize ANSI escapes).
+
+        - Any object with 'write' and 'flush' attributes.
+        """
+        return sys.stdout if self._ostream is None else self._ostream
+
+    def _set_ostream(self, val):
+        assert val is None or (hasattr(val, 'write') and hasattr(val, 'flush'))
+        self._ostream = val
+
+    ostream = property(_get_ostream, _set_ostream)
+
+    def set_colors(self, *args, **kw):
+        """Shorthand access to the color table scheme selector method."""
+
+        # Set own color table
+        self.color_scheme_table.set_active_scheme(*args, **kw)
+        # for convenience, set Colors to the active scheme
+        self.Colors = self.color_scheme_table.active_colors
+        # Also set colors of debugger
+        if hasattr(self, 'pdb') and self.pdb is not None:
+            self.pdb.set_colors(*args, **kw)
+
+    def color_toggle(self):
+        """Toggle between the currently active color scheme and NoColor."""
+
+        if self.color_scheme_table.active_scheme_name == 'NoColor':
+            self.color_scheme_table.set_active_scheme(self.old_scheme)
+            self.Colors = self.color_scheme_table.active_colors
+        else:
+            self.old_scheme = self.color_scheme_table.active_scheme_name
+            self.color_scheme_table.set_active_scheme('NoColor')
+            self.Colors = self.color_scheme_table.active_colors
+
+    def stb2text(self, stb):
+        """Convert a structured traceback (a list) to a string."""
+        return '\n'.join(stb)
+
+    def text(self, etype, value, tb, tb_offset=None, context=5):
+        """Return formatted traceback.
+
+        Subclasses may override this if they add extra arguments.
+        """
+        tb_list = self.structured_traceback(etype, value, tb,
+                                            tb_offset, context)
+        return self.stb2text(tb_list)
+
+    def structured_traceback(self, etype, evalue, tb, tb_offset=None,
+                             context=5, mode=None):
+        """Return a list of traceback frames.
+
+        Must be implemented by each class.
+        """
+        raise NotImplementedError()
+
+
+#---------------------------------------------------------------------------
+class ListTB(TBTools):
+    """Print traceback information from a traceback list, with optional color.
+
+    Calling requires 3 arguments: (etype, evalue, elist)
+    as would be obtained by::
+    
+      etype, evalue, tb = sys.exc_info()
+      if tb:
+        elist = traceback.extract_tb(tb)
+      else:
+        elist = None
+
+    It can thus be used by programs which need to process the traceback before
+    printing (such as console replacements based on the code module from the
+    standard library).
+
+    Because they are meant to be called without a full traceback (only a
+    list), instances of this class can't call the interactive pdb debugger."""
+
+    def __init__(self, color_scheme='NoColor', call_pdb=False, ostream=None, parent=None):
+        TBTools.__init__(self, color_scheme=color_scheme, call_pdb=call_pdb,
+                         ostream=ostream, parent=parent)
+
+    def __call__(self, etype, value, elist):
+        self.ostream.flush()
+        self.ostream.write(self.text(etype, value, elist))
+        self.ostream.write('\n')
+
+    def structured_traceback(self, etype, value, elist, tb_offset=None,
+                             context=5):
+        """Return a color formatted string with the traceback info.
+
+        Parameters
+        ----------
+        etype : exception type
+          Type of the exception raised.
+
+        value : object
+          Data stored in the exception
+
+        elist : list
+          List of frames, see class docstring for details.
+
+        tb_offset : int, optional
+          Number of frames in the traceback to skip.  If not given, the
+          instance value is used (set in constructor).
+
+        context : int, optional
+          Number of lines of context information to print.
+
+        Returns
+        -------
+        String with formatted exception.
+        """
+        tb_offset = self.tb_offset if tb_offset is None else tb_offset
+        Colors = self.Colors
+        out_list = []
+        if elist:
+
+            if tb_offset and len(elist) > tb_offset:
+                elist = elist[tb_offset:]
+
+            out_list.append('Traceback %s(most recent call last)%s:' %
+                            (Colors.normalEm, Colors.Normal) + '\n')
+            out_list.extend(self._format_list(elist))
+        # The exception info should be a single entry in the list.
+        lines = ''.join(self._format_exception_only(etype, value))
+        out_list.append(lines)
+
+        # Note: this code originally read:
+
+        ## for line in lines[:-1]:
+        ##     out_list.append(" "+line)
+        ## out_list.append(lines[-1])
+
+        # This means it was indenting everything but the last line by a little
+        # bit.  I've disabled this for now, but if we see ugliness somewhere we
+        # can restore it.
+
+        return out_list
+
+    def _format_list(self, extracted_list):
+        """Format a list of traceback entry tuples for printing.
+
+        Given a list of tuples as returned by extract_tb() or
+        extract_stack(), return a list of strings ready for printing.
+        Each string in the resulting list corresponds to the item with the
+        same index in the argument list.  Each string ends in a newline;
+        the strings may contain internal newlines as well, for those items
+        whose source text line is not None.
+
+        Lifted almost verbatim from traceback.py
+        """
+
+        Colors = self.Colors
+        list = []
+        for filename, lineno, name, line in extracted_list[:-1]:
+            item = '  File %s"%s"%s, line %s%d%s, in %s%s%s\n' % \
+                   (Colors.filename, py3compat.cast_unicode_py2(filename, "utf-8"), Colors.Normal,
+                    Colors.lineno, lineno, Colors.Normal,
+                    Colors.name, py3compat.cast_unicode_py2(name, "utf-8"), Colors.Normal)
+            if line:
+                item += '    %s\n' % line.strip()
+            list.append(item)
+        # Emphasize the last entry
+        filename, lineno, name, line = extracted_list[-1]
+        item = '%s  File %s"%s"%s, line %s%d%s, in %s%s%s%s\n' % \
+               (Colors.normalEm,
+                Colors.filenameEm, py3compat.cast_unicode_py2(filename, "utf-8"), Colors.normalEm,
+                Colors.linenoEm, lineno, Colors.normalEm,
+                Colors.nameEm, py3compat.cast_unicode_py2(name, "utf-8"), Colors.normalEm,
+                Colors.Normal)
+        if line:
+            item += '%s    %s%s\n' % (Colors.line, line.strip(),
+                                      Colors.Normal)
+        list.append(item)
+        return list
+
+    def _format_exception_only(self, etype, value):
+        """Format the exception part of a traceback.
+
+        The arguments are the exception type and value such as given by
+        sys.exc_info()[:2]. The return value is a list of strings, each ending
+        in a newline.  Normally, the list contains a single string; however,
+        for SyntaxError exceptions, it contains several lines that (when
+        printed) display detailed information about where the syntax error
+        occurred.  The message indicating which exception occurred is the
+        always last string in the list.
+
+        Also lifted nearly verbatim from traceback.py
+        """
+        have_filedata = False
+        Colors = self.Colors
+        list = []
+        stype = py3compat.cast_unicode(Colors.excName + etype.__name__ + Colors.Normal)
+        if value is None:
+            # Not sure if this can still happen in Python 2.6 and above
+            list.append(stype + '\n')
+        else:
+            if issubclass(etype, SyntaxError):
+                have_filedata = True
+                if not value.filename: value.filename = "<string>"
+                if value.lineno:
+                    lineno = value.lineno
+                    textline = ulinecache.getline(value.filename, value.lineno)
+                else:
+                    lineno = 'unknown'
+                    textline = ''
+                list.append('%s  File %s"%s"%s, line %s%s%s\n' % \
+                            (Colors.normalEm,
+                             Colors.filenameEm, py3compat.cast_unicode(value.filename), Colors.normalEm,
+                             Colors.linenoEm, lineno, Colors.Normal  ))
+                if textline == '':
+                    textline = py3compat.cast_unicode(value.text, "utf-8")
+
+                if textline is not None:
+                    i = 0
+                    while i < len(textline) and textline[i].isspace():
+                        i += 1
+                    list.append('%s    %s%s\n' % (Colors.line,
+                                                  textline.strip(),
+                                                  Colors.Normal))
+                    if value.offset is not None:
+                        s = '    '
+                        for c in textline[i:value.offset - 1]:
+                            if c.isspace():
+                                s += c
+                            else:
+                                s += ' '
+                        list.append('%s%s^%s\n' % (Colors.caret, s,
+                                                   Colors.Normal))
+
+            try:
+                s = value.msg
+            except Exception:
+                s = self._some_str(value)
+            if s:
+                list.append('%s%s:%s %s\n' % (stype, Colors.excName,
+                                              Colors.Normal, s))
+            else:
+                list.append('%s\n' % stype)
+
+        # sync with user hooks
+        if have_filedata:
+            ipinst = get_ipython()
+            if ipinst is not None:
+                ipinst.hooks.synchronize_with_editor(value.filename, value.lineno, 0)
+
+        return list
+
+    def get_exception_only(self, etype, value):
+        """Only print the exception type and message, without a traceback.
+
+        Parameters
+        ----------
+        etype : exception type
+        value : exception value
+        """
+        return ListTB.structured_traceback(self, etype, value, [])
+
+    def show_exception_only(self, etype, evalue):
+        """Only print the exception type and message, without a traceback.
+
+        Parameters
+        ----------
+        etype : exception type
+        value : exception value
+        """
+        # This method needs to use __call__ from *this* class, not the one from
+        # a subclass whose signature or behavior may be different
+        ostream = self.ostream
+        ostream.flush()
+        ostream.write('\n'.join(self.get_exception_only(etype, evalue)))
+        ostream.flush()
+
+    def _some_str(self, value):
+        # Lifted from traceback.py
+        try:
+            return py3compat.cast_unicode(str(value))
+        except:
+            return u'<unprintable %s object>' % type(value).__name__
+
+
+#----------------------------------------------------------------------------
+class VerboseTB(TBTools):
+    """A port of Ka-Ping Yee's cgitb.py module that outputs color text instead
+    of HTML.  Requires inspect and pydoc.  Crazy, man.
+
+    Modified version which optionally strips the topmost entries from the
+    traceback, to be used with alternate interpreters (because their own code
+    would appear in the traceback)."""
+
+    def __init__(self, color_scheme='Linux', call_pdb=False, ostream=None,
+                 tb_offset=0, long_header=False, include_vars=True,
+                 check_cache=None, debugger_cls = None):
+        """Specify traceback offset, headers and color scheme.
+
+        Define how many frames to drop from the tracebacks. Calling it with
+        tb_offset=1 allows use of this handler in interpreters which will have
+        their own code at the top of the traceback (VerboseTB will first
+        remove that frame before printing the traceback info)."""
+        TBTools.__init__(self, color_scheme=color_scheme, call_pdb=call_pdb,
+                         ostream=ostream)
+        self.tb_offset = tb_offset
+        self.long_header = long_header
+        self.include_vars = include_vars
+        # By default we use linecache.checkcache, but the user can provide a
+        # different check_cache implementation.  This is used by the IPython
+        # kernel to provide tracebacks for interactive code that is cached,
+        # by a compiler instance that flushes the linecache but preserves its
+        # own code cache.
+        if check_cache is None:
+            check_cache = linecache.checkcache
+        self.check_cache = check_cache
+
+        self.debugger_cls = debugger_cls or debugger.Pdb
+
+    def format_records(self, records, last_unique, recursion_repeat):
+        """Format the stack frames of the traceback"""
+        frames = []
+        for r in records[:last_unique+recursion_repeat+1]:
+            #print '*** record:',file,lnum,func,lines,index  # dbg
+            frames.append(self.format_record(*r))
+
+        if recursion_repeat:
+            frames.append('... last %d frames repeated, from the frame below ...\n' % recursion_repeat)
+            frames.append(self.format_record(*records[last_unique+recursion_repeat+1]))
+
+        return frames
+
+    def format_record(self, frame, file, lnum, func, lines, index):
+        """Format a single stack frame"""
+        Colors = self.Colors  # just a shorthand + quicker name lookup
+        ColorsNormal = Colors.Normal  # used a lot
+        col_scheme = self.color_scheme_table.active_scheme_name
+        indent = ' ' * INDENT_SIZE
+        em_normal = '%s\n%s%s' % (Colors.valEm, indent, ColorsNormal)
+        undefined = '%sundefined%s' % (Colors.em, ColorsNormal)
+        tpl_link = '%s%%s%s' % (Colors.filenameEm, ColorsNormal)
+        tpl_call = 'in %s%%s%s%%s%s' % (Colors.vName, Colors.valEm,
+                                        ColorsNormal)
+        tpl_call_fail = 'in %s%%s%s(***failed resolving arguments***)%s' % \
+                        (Colors.vName, Colors.valEm, ColorsNormal)
+        tpl_local_var = '%s%%s%s' % (Colors.vName, ColorsNormal)
+        tpl_global_var = '%sglobal%s %s%%s%s' % (Colors.em, ColorsNormal,
+                                                 Colors.vName, ColorsNormal)
+        tpl_name_val = '%%s %s= %%s%s' % (Colors.valEm, ColorsNormal)
+
+        tpl_line = '%s%%s%s %%s' % (Colors.lineno, ColorsNormal)
+        tpl_line_em = '%s%%s%s %%s%s' % (Colors.linenoEm, Colors.line,
+                                         ColorsNormal)
+
+        abspath = os.path.abspath
+
+
+        if not file:
+            file = '?'
+        elif file.startswith(str("<")) and file.endswith(str(">")):
+            # Not a real filename, no problem...
+            pass
+        elif not os.path.isabs(file):
+            # Try to make the filename absolute by trying all
+            # sys.path entries (which is also what linecache does)
+            for dirname in sys.path:
+                try:
+                    fullname = os.path.join(dirname, file)
+                    if os.path.isfile(fullname):
+                        file = os.path.abspath(fullname)
+                        break
+                except Exception:
+                    # Just in case that sys.path contains very
+                    # strange entries...
+                    pass
+
+        file = py3compat.cast_unicode(file, util_path.fs_encoding)
+        link = tpl_link % file
+        args, varargs, varkw, locals = fixed_getargvalues(frame)
+
+        if func == '?':
+            call = ''
+        else:
+            # Decide whether to include variable details or not
+            var_repr = self.include_vars and eqrepr or nullrepr
+            try:
+                call = tpl_call % (func, inspect.formatargvalues(args,
+                                                                 varargs, varkw,
+                                                                 locals, formatvalue=var_repr))
+            except KeyError:
+                # This happens in situations like errors inside generator
+                # expressions, where local variables are listed in the
+                # line, but can't be extracted from the frame.  I'm not
+                # 100% sure this isn't actually a bug in inspect itself,
+                # but since there's no info for us to compute with, the
+                # best we can do is report the failure and move on.  Here
+                # we must *not* call any traceback construction again,
+                # because that would mess up use of %debug later on.  So we
+                # simply report the failure and move on.  The only
+                # limitation will be that this frame won't have locals
+                # listed in the call signature.  Quite subtle problem...
+                # I can't think of a good way to validate this in a unit
+                # test, but running a script consisting of:
+                #  dict( (k,v.strip()) for (k,v) in range(10) )
+                # will illustrate the error, if this exception catch is
+                # disabled.
+                call = tpl_call_fail % func
+
+        # Don't attempt to tokenize binary files.
+        if file.endswith(('.so', '.pyd', '.dll')):
+            return '%s %s\n' % (link, call)
+
+        elif file.endswith(('.pyc', '.pyo')):
+            # Look up the corresponding source file.
+            try:
+                file = openpy.source_from_cache(file)
+            except ValueError:
+                # Failed to get the source file for some reason
+                # E.g. https://github.com/ipython/ipython/issues/9486
+                return '%s %s\n' % (link, call)
+
+        def linereader(file=file, lnum=[lnum], getline=ulinecache.getline):
+            line = getline(file, lnum[0])
+            lnum[0] += 1
+            return line
+
+        # Build the list of names on this line of code where the exception
+        # occurred.
+        try:
+            names = []
+            name_cont = False
+
+            for token_type, token, start, end, line in generate_tokens(linereader):
+                # build composite names
+                if token_type == tokenize.NAME and token not in keyword.kwlist:
+                    if name_cont:
+                        # Continuation of a dotted name
+                        try:
+                            names[-1].append(token)
+                        except IndexError:
+                            names.append([token])
+                        name_cont = False
+                    else:
+                        # Regular new names.  We append everything, the caller
+                        # will be responsible for pruning the list later.  It's
+                        # very tricky to try to prune as we go, b/c composite
+                        # names can fool us.  The pruning at the end is easy
+                        # to do (or the caller can print a list with repeated
+                        # names if so desired.
+                        names.append([token])
+                elif token == '.':
+                    name_cont = True
+                elif token_type == tokenize.NEWLINE:
+                    break
+
+        except (IndexError, UnicodeDecodeError, SyntaxError):
+            # signals exit of tokenizer
+            # SyntaxError can occur if the file is not actually Python
+            #  - see gh-6300
+            pass
+        except tokenize.TokenError as msg:
+            _m = ("An unexpected error occurred while tokenizing input\n"
+                  "The following traceback may be corrupted or invalid\n"
+                  "The error message is: %s\n" % msg)
+            error(_m)
+
+        # Join composite names (e.g. "dict.fromkeys")
+        names = ['.'.join(n) for n in names]
+        # prune names list of duplicates, but keep the right order
+        unique_names = uniq_stable(names)
+
+        # Start loop over vars
+        lvals = []
+        if self.include_vars:
+            for name_full in unique_names:
+                name_base = name_full.split('.', 1)[0]
+                if name_base in frame.f_code.co_varnames:
+                    if name_base in locals:
+                        try:
+                            value = repr(eval(name_full, locals))
+                        except:
+                            value = undefined
+                    else:
+                        value = undefined
+                    name = tpl_local_var % name_full
+                else:
+                    if name_base in frame.f_globals:
+                        try:
+                            value = repr(eval(name_full, frame.f_globals))
+                        except:
+                            value = undefined
+                    else:
+                        value = undefined
+                    name = tpl_global_var % name_full
+                lvals.append(tpl_name_val % (name, value))
+        if lvals:
+            lvals = '%s%s' % (indent, em_normal.join(lvals))
+        else:
+            lvals = ''
+
+        level = '%s %s\n' % (link, call)
+
+        if index is None:
+            return level
+        else:
+            return '%s%s' % (level, ''.join(
+                _format_traceback_lines(lnum, index, lines, Colors, lvals,
+                                        col_scheme)))
+
+    def prepare_chained_exception_message(self, cause):
+        direct_cause = "\nThe above exception was the direct cause of the following exception:\n"
+        exception_during_handling = "\nDuring handling of the above exception, another exception occurred:\n"
+
+        if cause:
+            message = [[direct_cause]]
+        else:
+            message = [[exception_during_handling]]
+        return message
+
+    def prepare_header(self, etype, long_version=False):
+        colors = self.Colors  # just a shorthand + quicker name lookup
+        colorsnormal = colors.Normal  # used a lot
+        exc = '%s%s%s' % (colors.excName, etype, colorsnormal)
+        width = min(75, get_terminal_size()[0])
+        if long_version:
+            # Header with the exception type, python version, and date
+            pyver = 'Python ' + sys.version.split()[0] + ': ' + sys.executable
+            date = time.ctime(time.time())
+
+            head = '%s%s%s\n%s%s%s\n%s' % (colors.topline, '-' * width, colorsnormal,
+                                           exc, ' ' * (width - len(str(etype)) - len(pyver)),
+                                           pyver, date.rjust(width) )
+            head += "\nA problem occurred executing Python code.  Here is the sequence of function" \
+                    "\ncalls leading up to the error, with the most recent (innermost) call last."
+        else:
+            # Simplified header
+            head = '%s%s' % (exc, 'Traceback (most recent call last)'. \
+                             rjust(width - len(str(etype))) )
+
+        return head
+
+    def format_exception(self, etype, evalue):
+        colors = self.Colors  # just a shorthand + quicker name lookup
+        colorsnormal = colors.Normal  # used a lot
+        indent = ' ' * INDENT_SIZE
+        # Get (safely) a string form of the exception info
+        try:
+            etype_str, evalue_str = map(str, (etype, evalue))
+        except:
+            # User exception is improperly defined.
+            etype, evalue = str, sys.exc_info()[:2]
+            etype_str, evalue_str = map(str, (etype, evalue))
+        # ... and format it
+        exception = ['%s%s%s: %s' % (colors.excName, etype_str,
+                                     colorsnormal, py3compat.cast_unicode(evalue_str))]
+
+        if (not py3compat.PY3) and type(evalue) is types.InstanceType:
+            try:
+                names = [w for w in dir(evalue) if isinstance(w, py3compat.string_types)]
+            except:
+                # Every now and then, an object with funny internals blows up
+                # when dir() is called on it.  We do the best we can to report
+                # the problem and continue
+                _m = '%sException reporting error (object with broken dir())%s:'
+                exception.append(_m % (colors.excName, colorsnormal))
+                etype_str, evalue_str = map(str, sys.exc_info()[:2])
+                exception.append('%s%s%s: %s' % (colors.excName, etype_str,
+                                                 colorsnormal, py3compat.cast_unicode(evalue_str)))
+                names = []
+            for name in names:
+                value = text_repr(getattr(evalue, name))
+                exception.append('\n%s%s = %s' % (indent, name, value))
+
+        return exception
+
+    def format_exception_as_a_whole(self, etype, evalue, etb, number_of_lines_of_context, tb_offset):
+        """Formats the header, traceback and exception message for a single exception.
+
+        This may be called multiple times by Python 3 exception chaining
+        (PEP 3134).
+        """
+        # some locals
+        orig_etype = etype
+        try:
+            etype = etype.__name__
+        except AttributeError:
+            pass
+
+        tb_offset = self.tb_offset if tb_offset is None else tb_offset
+        head = self.prepare_header(etype, self.long_header)
+        records = self.get_records(etb, number_of_lines_of_context, tb_offset)
+
+        if records is None:
+            return ""
+
+        last_unique, recursion_repeat = find_recursion(orig_etype, evalue, records)
+
+        frames = self.format_records(records, last_unique, recursion_repeat)
+
+        formatted_exception = self.format_exception(etype, evalue)
+        if records:
+            filepath, lnum = records[-1][1:3]
+            filepath = os.path.abspath(filepath)
+            ipinst = get_ipython()
+            if ipinst is not None:
+                ipinst.hooks.synchronize_with_editor(filepath, lnum, 0)
+
+        return [[head] + frames + [''.join(formatted_exception[0])]]
+
+    def get_records(self, etb, number_of_lines_of_context, tb_offset):
+        try:
+            # Try the default getinnerframes and Alex's: Alex's fixes some
+            # problems, but it generates empty tracebacks for console errors
+            # (5 blanks lines) where none should be returned.
+            return _fixed_getinnerframes(etb, number_of_lines_of_context, tb_offset)
+        except UnicodeDecodeError:
+            # This can occur if a file's encoding magic comment is wrong.
+            # I can't see a way to recover without duplicating a bunch of code
+            # from the stdlib traceback module. --TK
+            error('\nUnicodeDecodeError while processing traceback.\n')
+            return None
+        except:
+            # FIXME: I've been getting many crash reports from python 2.3
+            # users, traceable to inspect.py.  If I can find a small test-case
+            # to reproduce this, I should either write a better workaround or
+            # file a bug report against inspect (if that's the real problem).
+            # So far, I haven't been able to find an isolated example to
+            # reproduce the problem.
+            inspect_error()
+            traceback.print_exc(file=self.ostream)
+            info('\nUnfortunately, your original traceback can not be constructed.\n')
+            return None
+
+    def get_parts_of_chained_exception(self, evalue):
+        def get_chained_exception(exception_value):
+            cause = getattr(exception_value, '__cause__', None)
+            if cause:
+                return cause
+            if getattr(exception_value, '__suppress_context__', False):
+                return None
+            return getattr(exception_value, '__context__', None)
+
+        chained_evalue = get_chained_exception(evalue)
+
+        if chained_evalue:
+            return chained_evalue.__class__, chained_evalue, chained_evalue.__traceback__
+
+    def structured_traceback(self, etype, evalue, etb, tb_offset=None,
+                             number_of_lines_of_context=5):
+        """Return a nice text document describing the traceback."""
+
+        formatted_exception = self.format_exception_as_a_whole(etype, evalue, etb, number_of_lines_of_context,
+                                                               tb_offset)
+
+        colors = self.Colors  # just a shorthand + quicker name lookup
+        colorsnormal = colors.Normal  # used a lot
+        head = '%s%s%s' % (colors.topline, '-' * min(75, get_terminal_size()[0]), colorsnormal)
+        structured_traceback_parts = [head]
+        if py3compat.PY3:
+            chained_exceptions_tb_offset = 0
+            lines_of_context = 3
+            formatted_exceptions = formatted_exception
+            exception = self.get_parts_of_chained_exception(evalue)
+            if exception:
+                formatted_exceptions += self.prepare_chained_exception_message(evalue.__cause__)
+                etype, evalue, etb = exception
+            else:
+                evalue = None
+            chained_exc_ids = set()
+            while evalue:
+                formatted_exceptions += self.format_exception_as_a_whole(etype, evalue, etb, lines_of_context,
+                                                                         chained_exceptions_tb_offset)
+                exception = self.get_parts_of_chained_exception(evalue)
+
+                if exception and not id(exception[1]) in chained_exc_ids:
+                    chained_exc_ids.add(id(exception[1])) # trace exception to avoid infinite 'cause' loop
+                    formatted_exceptions += self.prepare_chained_exception_message(evalue.__cause__)
+                    etype, evalue, etb = exception
+                else:
+                    evalue = None
+
+            # we want to see exceptions in a reversed order:
+            # the first exception should be on top
+            for formatted_exception in reversed(formatted_exceptions):
+                structured_traceback_parts += formatted_exception
+        else:
+            structured_traceback_parts += formatted_exception[0]
+
+        return structured_traceback_parts
+
+    def debugger(self, force=False):
+        """Call up the pdb debugger if desired, always clean up the tb
+        reference.
+
+        Keywords:
+
+          - force(False): by default, this routine checks the instance call_pdb
+            flag and does not actually invoke the debugger if the flag is false.
+            The 'force' option forces the debugger to activate even if the flag
+            is false.
+
+        If the call_pdb flag is set, the pdb interactive debugger is
+        invoked. In all cases, the self.tb reference to the current traceback
+        is deleted to prevent lingering references which hamper memory
+        management.
+
+        Note that each call to pdb() does an 'import readline', so if your app
+        requires a special setup for the readline completers, you'll have to
+        fix that by hand after invoking the exception handler."""
+
+        if force or self.call_pdb:
+            if self.pdb is None:
+                self.pdb = self.debugger_cls()
+            # the system displayhook may have changed, restore the original
+            # for pdb
+            display_trap = DisplayTrap(hook=sys.__displayhook__)
+            with display_trap:
+                self.pdb.reset()
+                # Find the right frame so we don't pop up inside ipython itself
+                if hasattr(self, 'tb') and self.tb is not None:
+                    etb = self.tb
+                else:
+                    etb = self.tb = sys.last_traceback
+                while self.tb is not None and self.tb.tb_next is not None:
+                    self.tb = self.tb.tb_next
+                if etb and etb.tb_next:
+                    etb = etb.tb_next
+                self.pdb.botframe = etb.tb_frame
+                self.pdb.interaction(self.tb.tb_frame, self.tb)
+
+        if hasattr(self, 'tb'):
+            del self.tb
+
+    def handler(self, info=None):
+        (etype, evalue, etb) = info or sys.exc_info()
+        self.tb = etb
+        ostream = self.ostream
+        ostream.flush()
+        ostream.write(self.text(etype, evalue, etb))
+        ostream.write('\n')
+        ostream.flush()
+
+    # Changed so an instance can just be called as VerboseTB_inst() and print
+    # out the right info on its own.
+    def __call__(self, etype=None, evalue=None, etb=None):
+        """This hook can replace sys.excepthook (for Python 2.1 or higher)."""
+        if etb is None:
+            self.handler()
+        else:
+            self.handler((etype, evalue, etb))
+        try:
+            self.debugger()
+        except KeyboardInterrupt:
+            print("\nKeyboardInterrupt")
+
+
+#----------------------------------------------------------------------------
+class FormattedTB(VerboseTB, ListTB):
+    """Subclass ListTB but allow calling with a traceback.
+
+    It can thus be used as a sys.excepthook for Python > 2.1.
+
+    Also adds 'Context' and 'Verbose' modes, not available in ListTB.
+
+    Allows a tb_offset to be specified. This is useful for situations where
+    one needs to remove a number of topmost frames from the traceback (such as
+    occurs with python programs that themselves execute other python code,
+    like Python shells).  """
+
+    def __init__(self, mode='Plain', color_scheme='Linux', call_pdb=False,
+                 ostream=None,
+                 tb_offset=0, long_header=False, include_vars=False,
+                 check_cache=None, debugger_cls=None):
+
+        # NEVER change the order of this list. Put new modes at the end:
+        self.valid_modes = ['Plain', 'Context', 'Verbose']
+        self.verbose_modes = self.valid_modes[1:3]
+
+        VerboseTB.__init__(self, color_scheme=color_scheme, call_pdb=call_pdb,
+                           ostream=ostream, tb_offset=tb_offset,
+                           long_header=long_header, include_vars=include_vars,
+                           check_cache=check_cache, debugger_cls=debugger_cls)
+
+        # Different types of tracebacks are joined with different separators to
+        # form a single string.  They are taken from this dict
+        self._join_chars = dict(Plain='', Context='\n', Verbose='\n')
+        # set_mode also sets the tb_join_char attribute
+        self.set_mode(mode)
+
+    def _extract_tb(self, tb):
+        if tb:
+            return traceback.extract_tb(tb)
+        else:
+            return None
+
+    def structured_traceback(self, etype, value, tb, tb_offset=None, number_of_lines_of_context=5):
+        tb_offset = self.tb_offset if tb_offset is None else tb_offset
+        mode = self.mode
+        if mode in self.verbose_modes:
+            # Verbose modes need a full traceback
+            return VerboseTB.structured_traceback(
+                self, etype, value, tb, tb_offset, number_of_lines_of_context
+            )
+        else:
+            # We must check the source cache because otherwise we can print
+            # out-of-date source code.
+            self.check_cache()
+            # Now we can extract and format the exception
+            elist = self._extract_tb(tb)
+            return ListTB.structured_traceback(
+                self, etype, value, elist, tb_offset, number_of_lines_of_context
+            )
+
+    def stb2text(self, stb):
+        """Convert a structured traceback (a list) to a string."""
+        return self.tb_join_char.join(stb)
+
+
+    def set_mode(self, mode=None):
+        """Switch to the desired mode.
+
+        If mode is not specified, cycles through the available modes."""
+
+        if not mode:
+            new_idx = (self.valid_modes.index(self.mode) + 1 ) % \
+                      len(self.valid_modes)
+            self.mode = self.valid_modes[new_idx]
+        elif mode not in self.valid_modes:
+            raise ValueError('Unrecognized mode in FormattedTB: <' + mode + '>\n'
+                                                                            'Valid modes: ' + str(self.valid_modes))
+        else:
+            self.mode = mode
+        # include variable details only in 'Verbose' mode
+        self.include_vars = (self.mode == self.valid_modes[2])
+        # Set the join character for generating text tracebacks
+        self.tb_join_char = self._join_chars[self.mode]
+
+    # some convenient shortcuts
+    def plain(self):
+        self.set_mode(self.valid_modes[0])
+
+    def context(self):
+        self.set_mode(self.valid_modes[1])
+
+    def verbose(self):
+        self.set_mode(self.valid_modes[2])
+
+
+#----------------------------------------------------------------------------
+class AutoFormattedTB(FormattedTB):
+    """A traceback printer which can be called on the fly.
+
+    It will find out about exceptions by itself.
+
+    A brief example::
+
+        AutoTB = AutoFormattedTB(mode = 'Verbose',color_scheme='Linux')
+        try:
+          ...
+        except:
+          AutoTB()  # or AutoTB(out=logfile) where logfile is an open file object
+    """
+
+    def __call__(self, etype=None, evalue=None, etb=None,
+                 out=None, tb_offset=None):
+        """Print out a formatted exception traceback.
+
+        Optional arguments:
+          - out: an open file-like object to direct output to.
+
+          - tb_offset: the number of frames to skip over in the stack, on a
+          per-call basis (this overrides temporarily the instance's tb_offset
+          given at initialization time.  """
+
+        if out is None:
+            out = self.ostream
+        out.flush()
+        out.write(self.text(etype, evalue, etb, tb_offset))
+        out.write('\n')
+        out.flush()
+        # FIXME: we should remove the auto pdb behavior from here and leave
+        # that to the clients.
+        try:
+            self.debugger()
+        except KeyboardInterrupt:
+            print("\nKeyboardInterrupt")
+
+    def structured_traceback(self, etype=None, value=None, tb=None,
+                             tb_offset=None, number_of_lines_of_context=5):
+        if etype is None:
+            etype, value, tb = sys.exc_info()
+        self.tb = tb
+        return FormattedTB.structured_traceback(
+            self, etype, value, tb, tb_offset, number_of_lines_of_context)
+
+
+#---------------------------------------------------------------------------
+
+# A simple class to preserve Nathan's original functionality.
+class ColorTB(FormattedTB):
+    """Shorthand to initialize a FormattedTB in Linux colors mode."""
+
+    def __init__(self, color_scheme='Linux', call_pdb=0, **kwargs):
+        FormattedTB.__init__(self, color_scheme=color_scheme,
+                             call_pdb=call_pdb, **kwargs)
+
+
+class SyntaxTB(ListTB):
+    """Extension which holds some state: the last exception value"""
+
+    def __init__(self, color_scheme='NoColor'):
+        ListTB.__init__(self, color_scheme)
+        self.last_syntax_error = None
+
+    def __call__(self, etype, value, elist):
+        self.last_syntax_error = value
+
+        ListTB.__call__(self, etype, value, elist)
+
+    def structured_traceback(self, etype, value, elist, tb_offset=None,
+                             context=5):
+        # If the source file has been edited, the line in the syntax error can
+        # be wrong (retrieved from an outdated cache). This replaces it with
+        # the current value.
+        if isinstance(value, SyntaxError) \
+                and isinstance(value.filename, py3compat.string_types) \
+                and isinstance(value.lineno, int):
+            linecache.checkcache(value.filename)
+            newtext = ulinecache.getline(value.filename, value.lineno)
+            if newtext:
+                value.text = newtext
+        self.last_syntax_error = value
+        return super(SyntaxTB, self).structured_traceback(etype, value, elist,
+                                                          tb_offset=tb_offset, context=context)
+
+    def clear_err_state(self):
+        """Return the current error state and clear it"""
+        e = self.last_syntax_error
+        self.last_syntax_error = None
+        return e
+
+    def stb2text(self, stb):
+        """Convert a structured traceback (a list) to a string."""
+        return ''.join(stb)
+
+
+# some internal-use functions
+def text_repr(value):
+    """Hopefully pretty robust repr equivalent."""
+    # this is pretty horrible but should always return *something*
+    try:
+        return pydoc.text.repr(value)
+    except KeyboardInterrupt:
+        raise
+    except:
+        try:
+            return repr(value)
+        except KeyboardInterrupt:
+            raise
+        except:
+            try:
+                # all still in an except block so we catch
+                # getattr raising
+                name = getattr(value, '__name__', None)
+                if name:
+                    # ick, recursion
+                    return text_repr(name)
+                klass = getattr(value, '__class__', None)
+                if klass:
+                    return '%s instance' % text_repr(klass)
+            except KeyboardInterrupt:
+                raise
+            except:
+                return 'UNRECOVERABLE REPR FAILURE'
+
+
+def eqrepr(value, repr=text_repr):
+    return '=%s' % repr(value)
+
+
+def nullrepr(value, repr=text_repr):
+    return ''