def structured_traceback(self, etype, evalue, etb, tb_offset=None,
                             context=5):

        tb_offset = self.tb_offset if tb_offset is None else tb_offset

        # some locals
        try:
            etype = etype.__name__
        except AttributeError:
            pass
        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)
        exc = '%s%s%s' % (Colors.excName,etype,ColorsNormal)

        # 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 ''

        # meat of the code begins
        try:
            etype = etype.__name__
        except AttributeError:
            pass

        if self.long_header:
            # 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, '-'*75, ColorsNormal,
                                           exc, ' '*(75-len(str(etype))-len(pyver)),
                                           pyver, date.rjust(75) )
            head += "\nA problem occured 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%s\n%s%s' % (Colors.topline, '-'*75, ColorsNormal,exc,
                                     'Traceback (most recent call last)'.\
                                        rjust(75 - len(str(etype)) ) )
        frames = []
        # Flush cache before calling inspect.  This helps alleviate some of the
        # problems with python 2.3's inspect.py.
        ##self.check_cache()
        # Drop topmost frames if requested
        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.
            #records = inspect.getinnerframes(etb, context)[tb_offset:]
            #print 'python records:', records # dbg
            records = _fixed_getinnerframes(etb, context, tb_offset)
            #print 'alex   records:', records # dbg
        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 ''

        # build some color string templates outside these nested loops
        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)

        # now, loop over all records printing context and info
        abspath = os.path.abspath
        for frame, file, lnum, func, lines, index in records:
            #print '*** record:',file,lnum,func,lines,index  # dbg
            try:
                file = file and abspath(file) or '?'
            except OSError:
                # if file is '<console>' or something not in the filesystem,
                # the abspath call will throw an OSError.  Just ignore it and
                # keep the original file string.
                pass
            link = tpl_link % file
            try:
                args, varargs, varkw, locals = inspect.getargvalues(frame)
            except:
                # This can happen due to a bug in python2.3.  We should be
                # able to remove this try/except when 2.4 becomes a
                # requirement.  Bug details at http://python.org/sf/1005466
                inspect_error()
                traceback.print_exc(file=self.ostream)
                info("\nIPython's exception reporting continues...\n")
                
            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

            # Initialize a list of names on the current line, which the
            # tokenizer below will populate.
            names = []

            def tokeneater(token_type, token, start, end, line):
                """Stateful tokeneater which builds dotted names.

                The list of names it appends to (from the enclosing scope) can
                contain repeated composite names.  This is unavoidable, since
                there is no way to disambguate partial dotted structures until
                the full list is known.  The caller is responsible for pruning
                the final list of duplicates before using it."""
                
                # build composite names
                if token == '.':
                    try:
                        names[-1] += '.'
                        # store state so the next token is added for x.y.z names
                        tokeneater.name_cont = True
                        return
                    except IndexError:
                        pass
                if token_type == tokenize.NAME and token not in keyword.kwlist:
                    if tokeneater.name_cont:
                        # Dotted names
                        names[-1] += token
                        tokeneater.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_type == tokenize.NEWLINE:
                    raise IndexError
            # we need to store a bit of state in the tokenizer to build
            # dotted names
            tokeneater.name_cont = False

            def linereader(file=file, lnum=[lnum], getline=linecache.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:
                # This builds the names list in-place by capturing it from the
                # enclosing scope.
                # We're using _tokenize because tokenize expects bytes, and
                # attempts to find an encoding cookie, which can go wrong
                # e.g. if the traceback line includes "encoding=encoding".
                # N.B. _tokenize is undocumented. An official API for
                # tokenising strings is proposed in Python Issue 9969.
                for atoken in tokenize._tokenize(linereader, None):
                    tokeneater(*atoken)
            except IndexError:
                # signals exit of tokenizer
                pass
            except UnicodeDecodeError:
                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)
            
            # 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:
                frames.append(level)
            else:
                frames.append('%s%s' % (level,''.join(
                    _format_traceback_lines(lnum,index,lines,Colors,lvals,
                                            col_scheme))))

        # Get (safely) a string form of the exception info
        try:
            etype_str,evalue_str = list(map(str,(etype,evalue)))
        except:
            # User exception is improperly defined.
            etype,evalue = str,sys.exc_info()[:2]
            etype_str,evalue_str = list(map(str,(etype,evalue)))
        # ... and format it
        exception = ['%s%s%s: %s' % (Colors.excName, etype_str,
                                     ColorsNormal, evalue_str)]

        # vds: >>
        if records:
             filepath, lnum = records[-1][1:3]
             #print "file:", str(file), "linenb", str(lnum) # dbg
             filepath = os.path.abspath(filepath)
             ipinst = ipapi.get()
             if ipinst is not None:
                 ipinst.hooks.synchronize_with_editor(filepath, lnum, 0)
        # vds: <<
                
        # return all our info assembled as a single string
        # return '%s\n\n%s\n%s' % (head,'\n'.join(frames),''.join(exception[0]) )
        return [head] + frames + [''.join(exception[0])]
Return a nice text document describing the traceback.
dataset/ETHPy150Open ipython/ipython-py3k/IPython/core/ultratb.py/VerboseTB.structured_traceback