text: """Extract, format and print information about Python stack traces."""
  
  # import collections
  # import itertools
  import linecache
  import sys
  
  __all__ = ['extract_stack', 'extract_tb', 'format_exception',
             'format_exception_only', 'format_list', 'format_stack',
             'format_tb', 'print_exc', 'format_exc', 'print_exception',
             'print_last', 'print_stack', 'print_tb', 'clear_frames',
             'FrameSummary', 'StackSummary', 'TracebackException',
             'walk_stack', 'walk_tb']
  
  #
  # Formatting and printing lists of traceback lines.
  #
  
  def print_list(extracted_list, file=None):
      """Print the list of tuples as returned by extract_tb() or
      extract_stack() as a formatted stack trace to the given file."""
      if file is None:
          file = sys.stderr
      for item in StackSummary.from_list(extracted_list).format():
          print(item, file=file, end="")
  
  def format_list(extracted_list):
      """Format a list of tuples or FrameSummary objects for printing.
  
      Given a list of tuples or FrameSummary objects 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.
      """
      return StackSummary.from_list(extracted_list).format()
  
  #
  # Printing and Extracting Tracebacks.
  #
  
  def print_tb(tb, limit=None, file=None):
      """Print up to 'limit' stack trace entries from the traceback 'tb'.
  
      If 'limit' is omitted or None, all entries are printed.  If 'file'
      is omitted or None, the output goes to sys.stderr; otherwise
      'file' should be an open file or file-like object with a write()
      method.
      """
      print_list(extract_tb(tb, limit=limit), file=file)
  
  def format_tb(tb, limit=None):
      """A shorthand for 'format_list(extract_tb(tb, limit))'."""
      return extract_tb(tb, limit=limit).format()
  
  def extract_tb(tb, limit=None):
      """
      Return a StackSummary object representing a list of
      pre-processed entries from traceback.
  
      This is useful for alternate formatting of stack traces.  If
      'limit' is omitted or None, all entries are extracted.  A
      pre-processed stack trace entry is a FrameSummary object
      containing attributes filename, lineno, name, and line
      representing the information that is usually printed for a stack
      trace.  The line is a string with leading and trailing
      whitespace stripped; if the source is not available it is None.
      """
      return StackSummary.extract(walk_tb(tb), limit=limit)
  
  #
  # Exception formatting and output.
  #
  
  _cause_message = (
      "\nThe above exception was the direct cause "
      "of the following exception:\n\n")
  
  _context_message = (
      "\nDuring handling of the above exception, "
      "another exception occurred:\n\n")
  
  
  class _Sentinel:
      def __repr__(self):
          return "<implicit>"
  
  _sentinel = _Sentinel()
  
  def _parse_value_tb(exc, value, tb):
      if (value is _sentinel) != (tb is _sentinel):
          raise ValueError("Both or neither of value and tb must be given")
      if value is tb is _sentinel:
          if exc is not None:
              return exc, exc.__traceback__
          else:
              return None, None
      return value, tb
  
  
  def print_exception(exc, /, value=_sentinel, tb=_sentinel, limit=None, \
                      file=None, chain=True):
      """Print exception up to 'limit' stack trace entries from 'tb' to 'file'.
  
      This differs from print_tb() in the following ways: (1) if
      traceback is not None, it prints a header "Traceback (most recent
      call last):"; (2) it prints the exception type and value after the
      stack trace; (3) if type is SyntaxError and value has the
      appropriate format, it prints the line where the syntax error
      occurred with a caret on the next line indicating the approximate
      position of the error.
      """
      value, tb = _parse_value_tb(exc, value, tb)
      if file is None:
          file = sys.stderr
      te = TracebackException(type(value), value, tb, limit=limit, compact=True)
      for line in te.format(chain=chain):
          print(line, file=file, end="")
  
  
  def format_exception(exc, /, value=_sentinel, tb=_sentinel, limit=None, \
                       chain=True):
      """Format a stack trace and the exception information.
  
      The arguments have the same meaning as the corresponding arguments
      to print_exception().  The return value is a list of strings, each
      ending in a newline and some containing internal newlines.  When
      these lines are concatenated and printed, exactly the same text is
      printed as does print_exception().
      """
      value, tb = _parse_value_tb(exc, value, tb)
      te = TracebackException(type(value), value, tb, limit=limit, compact=True)
      return list(te.format(chain=chain))
  
  
  def format_exception_only(exc, /, value=_sentinel):
      """Format the exception part of a traceback.
  
      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 always the last
      string in the list.
  
      """
      if value is _sentinel:
          value = exc
      te = TracebackException(type(value), value, None, compact=True)
      return list(te.format_exception_only())
  
  
  # -- not official API but folk probably use these two functions.
  
  def _format_final_exc_line(etype, value):
      valuestr = _some_str(value)
      if value is None or not valuestr:
          line = "%s\n" % etype
      else:
          line = "%s: %s\n" % (etype, valuestr)
      return line
  
  def _some_str(value):
      try:
          return str(value)
      except:
          return '<unprintable %s object>' % type(value).__name__
  
  # --
  
  def print_exc(limit=None, file=None, chain=True):
      """Shorthand for 'print_exception(*sys.exc_info(), limit, file)'."""
      print_exception(*sys.exc_info(), limit=limit, file=file, chain=chain)
  
  def format_exc(limit=None, chain=True):
      """Like print_exc() but return a string."""
      return "".join(format_exception(*sys.exc_info(), limit=limit, chain=chain))
  
  def print_last(limit=None, file=None, chain=True):
      """This is a shorthand for 'print_exception(sys.last_type,
      sys.last_value, sys.last_traceback, limit, file)'."""
      if not hasattr(sys, "last_type"):
          raise ValueError("no last exception")
      print_exception(sys.last_type, sys.last_value, sys.last_traceback,
                      limit, file, chain)
  
  #
  # Printing and Extracting Stacks.
  #
  
  def print_stack(f=None, limit=None, file=None):
      """Print a stack trace from its invocation point.
  
      The optional 'f' argument can be used to specify an alternate
      stack frame at which to start. The optional 'limit' and 'file'
      arguments have the same meaning as for print_exception().
      """
      if f is None:
          f = sys._getframe().f_back
      print_list(extract_stack(f, limit=limit), file=file)
  
  
  def format_stack(f=None, limit=None):
      """Shorthand for 'format_list(extract_stack(f, limit))'."""
      if f is None:
          f = sys._getframe().f_back
      return format_list(extract_stack(f, limit=limit))
  
  
  def extract_stack(f=None, limit=None):
      """Extract the raw traceback from the current stack frame.
  
      The return value has the same format as for extract_tb().  The
      optional 'f' and 'limit' arguments have the same meaning as for
      print_stack().  Each item in the list is a quadruple (filename,
      line number, function name, text), and the entries are in order
      from oldest to newest stack frame.
      """
      if f is None:
          f = sys._getframe().f_back
      stack = StackSummary.extract(walk_stack(f), limit=limit)
      stack.reverse()
      return stack
  
  
  def clear_frames(tb):
      "Clear all references to local variables in the frames of a traceback."
      while tb is not None:
          try:
              tb.tb_frame.clear()
          except RuntimeError:
              # Ignore the exception raised if the frame is still executing.
              pass
          tb = tb.tb_next
  
  
  class FrameSummary:
      """A single frame from a traceback.
  
      - :attr:`filename` The filename for the frame.
      - :attr:`lineno` The line within filename for the frame that was
        active when the frame was captured.
      - :attr:`name` The name of the function or method that was executing
        when the frame was captured.
      - :attr:`line` The text from the linecache module for the
        of code that was running when the frame was captured.
      - :attr:`locals` Either None if locals were not supplied, or a dict
        mapping the name to the repr() of the variable.
      """
  
      __slots__ = ('filename', 'lineno', 'name', '_line', 'locals')
  
      def __init__(self, filename, lineno, name, *, lookup_line=True,
              locals=None, line=None):
          """Construct a FrameSummary.
  
          :param lookup_line: If True, `linecache` is consulted for the source
              code line. Otherwise, the line will be looked up when first needed.
          :param locals: If supplied the frame locals, which will be captured as
              object representations.
          :param line: If provided, use this instead of looking up the line in
              the linecache.
          """
          self.filename = filename
          self.lineno = lineno
          self.name = name
          self._line = line
          if lookup_line:
              self.line
          self.locals = {k: repr(v) for k, v in locals.items()} if locals else None
  
      def __eq__(self, other):
          if isinstance(other, FrameSummary):
              return (self.filename == other.filename and
                      self.lineno == other.lineno and
                      self.name == other.name and
                      self.locals == other.locals)
          if isinstance(other, tuple):
              return (self.filename, self.lineno, self.name, self.line) == other
          return NotImplemented
  
      def __getitem__(self, pos):
          return (self.filename, self.lineno, self.name, self.line)[pos]
  
      def __iter__(self):
          return iter([self.filename, self.lineno, self.name, self.line])
  
      def __repr__(self):
          return "<FrameSummary file {filename}, line {lineno} in {name}>".format(
              filename=self.filename, lineno=self.lineno, name=self.name)
  
      def __len__(self):
          return 4
  
      @property
      def line(self):
          if self._line is None:
              if self.lineno is None:
                  return None
              self._line = linecache.getline(self.filename, self.lineno)
          return self._line.strip()
  
  def walk_stack(f):
      """Walk a stack yielding the frame and line number for each frame.
  
      This will follow f.f_back from the given frame. If no frame is given, the
      current stack is used. Usually used with StackSummary.extract.
      """
      if f is None:
          f = sys._getframe().f_back.f_back
      while f is not None:
          yield f, f.f_lineno
          f = f.f_back
  
  
  def walk_tb(tb):
      """Walk a traceback yielding the frame and line number for each frame.
  
      This will follow tb.tb_next (and thus is in the opposite order to
      walk_stack). Usually used with StackSummary.extract.
      """
      while tb is not None:
          yield tb.tb_frame, tb.tb_lineno
          tb = tb.tb_next
  
  
  _RECURSIVE_CUTOFF = 3 # Also hardcoded in traceback.c.
  
  class StackSummary(list):
      """A stack of frames."""
  
      @classmethod
      def extract(klass, frame_gen, *, limit=None, lookup_lines=True,
              capture_locals=False):
          """Create a StackSummary from a traceback or stack object.
  
          :param frame_gen: A generator that yields (frame, lineno) tuples to
              include in the stack.
          :param limit: None to include all frames or the number of frames to
              include.
          :param lookup_lines: If True, lookup lines for each frame immediately,
              otherwise lookup is deferred until the frame is rendered.
          :param capture_locals: If True, the local variables from each frame will
              be captured as object representations into the FrameSummary.
          """
          if limit is None:
              limit = getattr(sys, 'tracebacklimit', None)
              if limit is not None and limit < 0:
                  limit = 0
          # if limit is not None:
              # if limit >= 0:
              #     frame_gen = itertools.islice(frame_gen, limit)
              # else:
              #     frame_gen = collections.deque(frame_gen, maxlen=-limit)
  
          result = klass()
          fnames = set()
          for f, lineno in frame_gen:
              co = f.f_code
              filename = co.co_filename
              name = co.co_name
  
              fnames.add(filename)
              linecache.lazycache(filename, f.f_globals)
              # Must defer line lookups until we have called checkcache.
              if capture_locals:
                  f_locals = f.f_locals
              else:
                  f_locals = None
              result.append(FrameSummary(
                  filename, lineno, name, lookup_line=False, locals=f_locals))
          for filename in fnames:
              linecache.checkcache(filename)
          # If immediate lookup was desired, trigger lookups now.
          if lookup_lines:
              for f in result:
                  f.line
          return result
  
      @classmethod
      def from_list(klass, a_list):
          """
          Create a StackSummary object from a supplied list of
          FrameSummary objects or old-style list of tuples.
          """
          # While doing a fast-path check for isinstance(a_list, StackSummary) is
          # appealing, idlelib.run.cleanup_traceback and other similar code may
          # break this by making arbitrary frames plain tuples, so we need to
          # check on a frame by frame basis.
          result = StackSummary()
          for frame in a_list:
              if isinstance(frame, FrameSummary):
                  result.append(frame)
              else:
                  filename, lineno, name, line = frame
                  result.append(FrameSummary(filename, lineno, name, line=line))
          return result
  
      def format(self):
          """Format the stack ready for printing.
  
          Returns a list of strings ready for printing.  Each string in the
          resulting list corresponds to a single frame from the stack.
          Each string ends in a newline; the strings may contain internal
          newlines as well, for those items with source text lines.
  
          For long sequences of the same frame and line, the first few
          repetitions are shown, followed by a summary line stating the exact
          number of further repetitions.
          """
          result = []
          last_file = None
          last_line = None
          last_name = None
          count = 0
          for frame in self:
              if (last_file is None or last_file != frame.filename or
                  last_line is None or last_line != frame.lineno or
                  last_name is None or last_name != frame.name):
                  if count > _RECURSIVE_CUTOFF:
                      count -= _RECURSIVE_CUTOFF
                      result.append(
                          f'  [Previous line repeated {count} more '
                          f'time{"s" if count > 1 else ""}]\n'
                      )
                  last_file = frame.filename
                  last_line = frame.lineno
                  last_name = frame.name
                  count = 0
              count += 1
              if count > _RECURSIVE_CUTOFF:
                  continue
              row = []
              row.append('  File "{}", line {}, in {}\n'.format(
                  frame.filename, frame.lineno, frame.name))
              if frame.line:
                  row.append('    {}\n'.format(frame.line.strip()))
              if frame.locals:
                  for name, value in sorted(frame.locals.items()):
                      row.append('    {name} = {value}\n'.format(name=name, value=value))
              result.append(''.join(row))
          if count > _RECURSIVE_CUTOFF:
              count -= _RECURSIVE_CUTOFF
              result.append(
                  f'  [Previous line repeated {count} more '
                  f'time{"s" if count > 1 else ""}]\n'
              )
          return result
  
  
  class TracebackException:
      """An exception ready for rendering.
  
      The traceback module captures enough attributes from the original exception
      to this intermediary form to ensure that no references are held, while
      still being able to fully print or format it.
  
      Use `from_exception` to create TracebackException instances from exception
      objects, or the constructor to create TracebackException instances from
      individual components.
  
      - :attr:`__cause__` A TracebackException of the original *__cause__*.
      - :attr:`__context__` A TracebackException of the original *__context__*.
      - :attr:`__suppress_context__` The *__suppress_context__* value from the
        original exception.
      - :attr:`stack` A `StackSummary` representing the traceback.
      - :attr:`exc_type` The class of the original traceback.
      - :attr:`filename` For syntax errors - the filename where the error
        occurred.
      - :attr:`lineno` For syntax errors - the linenumber where the error
        occurred.
      - :attr:`text` For syntax errors - the text where the error
        occurred.
      - :attr:`offset` For syntax errors - the offset into the text where the
        error occurred.
      - :attr:`msg` For syntax errors - the compiler error message.
      """
  
      def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
              lookup_lines=True, capture_locals=False, compact=False,
              _seen=None):
          # NB: we need to accept exc_traceback, exc_value, exc_traceback to
          # permit backwards compat with the existing API, otherwise we
          # need stub thunk objects just to glue it together.
          # Handle loops in __cause__ or __context__.
          is_recursive_call = _seen is not None
          if _seen is None:
              _seen = set()
          _seen.add(id(exc_value))
  
          # TODO: locals.
          self.stack = StackSummary.extract(
              walk_tb(exc_traceback), limit=limit, lookup_lines=lookup_lines,
              capture_locals=capture_locals)
          self.exc_type = exc_type
          # Capture now to permit freeing resources: only complication is in the
          # unofficial API _format_final_exc_line
          self._str = _some_str(exc_value)
          if exc_type and issubclass(exc_type, SyntaxError):
              # Handle SyntaxError's specially
              self.filename = exc_value.filename
              lno = exc_value.lineno
              self.lineno = str(lno) if lno is not None else None
              self.text = exc_value.text
              self.offset = exc_value.offset
              self.msg = exc_value.msg
          if lookup_lines:
              self._load_lines()
          self.__suppress_context__ = \
              exc_value.__suppress_context__ if exc_value is not None else False
  
          # Convert __cause__ and __context__ to `TracebackExceptions`s, use a
          # queue to avoid recursion (only the top-level call gets _seen == None)
          if not is_recursive_call:
              queue = [(self, exc_value)]
              while queue:
                  te, e = queue.pop()
                  if (e and e.__cause__ is not None
                      and id(e.__cause__) not in _seen):
                      cause = TracebackException(
                          type(e.__cause__),
                          e.__cause__,
                          e.__cause__.__traceback__,
                          limit=limit,
                          lookup_lines=lookup_lines,
                          capture_locals=capture_locals,
                          _seen=_seen)
                  else:
                      cause = None
  
                  if compact:
                      need_context = (cause is None and
                                      e is not None and
                                      not e.__suppress_context__)
                  else:
                      need_context = True
                  if (e and e.__context__ is not None
                      and need_context and id(e.__context__) not in _seen):
                      context = TracebackException(
                          type(e.__context__),
                          e.__context__,
                          e.__context__.__traceback__,
                          limit=limit,
                          lookup_lines=lookup_lines,
                          capture_locals=capture_locals,
                          _seen=_seen)
                  else:
                      context = None
                  te.__cause__ = cause
                  te.__context__ = context
                  if cause:
                      queue.append((te.__cause__, e.__cause__))
                  if context:
                      queue.append((te.__context__, e.__context__))
  
      @classmethod
      def from_exception(cls, exc, *args, **kwargs):
          """Create a TracebackException from an exception."""
          return cls(type(exc), exc, exc.__traceback__, *args, **kwargs)
  
      def _load_lines(self):
          """Private API. force all lines in the stack to be loaded."""
          for frame in self.stack:
              frame.line
  
      def __eq__(self, other):
          if isinstance(other, TracebackException):
              return self.__dict__ == other.__dict__
          return NotImplemented
  
      def __str__(self):
          return self._str
  
      def format_exception_only(self):
          """Format the exception part of the traceback.
  
          The return value is a generator of strings, each ending in a newline.
  
          Normally, the generator emits a single string; however, for
          SyntaxError exceptions, it emits several lines that (when
          printed) display detailed information about where the syntax
          error occurred.
  
          The message indicating which exception occurred is always the last
          string in the output.
          """
          if self.exc_type is None:
              yield _format_final_exc_line(None, self._str)
              return
  
          stype = self.exc_type.__qualname__
          smod = self.exc_type.__module__
          if smod not in ("__main__", "builtins"):
              stype = smod + '.' + stype
  
          if not issubclass(self.exc_type, SyntaxError):
              yield _format_final_exc_line(stype, self._str)
          else:
              yield from self._format_syntax_error(stype)
  
      def _format_syntax_error(self, stype):
          """Format SyntaxError exceptions (internal helper)."""
          # Show exactly where the problem was found.
          filename_suffix = ''
          if self.lineno is not None:
              yield '  File "{}", line {}\n'.format(
                  self.filename or "<string>", self.lineno)
          elif self.filename is not None:
              filename_suffix = ' ({})'.format(self.filename)
  
          text = self.text
          if text is not None:
              # text  = "   foo\n"
              # rtext = "   foo"
              # ltext =    "foo"
              rtext = text.rstrip('\n')
              ltext = rtext.lstrip(' \n\f')
              spaces = len(rtext) - len(ltext)
              yield '    {}\n'.format(ltext)
              # Convert 1-based column offset to 0-based index into stripped text
              caret = (self.offset or 0) - 1 - spaces
              if caret >= 0:
                  # non-space whitespace (likes tabs) must be kept for alignment
                  caretspace = ((c if c.isspace() else ' ') for c in ltext[:caret])
                  yield '    {}^\n'.format(''.join(caretspace))
          msg = self.msg or "<no detail available>"
          yield "{}: {}{}\n".format(stype, msg, filename_suffix)
  
      def format(self, *, chain=True):
          """Format the exception.
  
          If chain is not *True*, *__cause__* and *__context__* will not be formatted.
  
          The return value is a generator of strings, each ending in a newline and
          some containing internal newlines. `print_exception` is a wrapper around
          this method which just prints the lines to a file.
  
          The message indicating which exception occurred is always the last
          string in the output.
          """
  
          output = []
          exc = self
          while exc:
              if chain:
                  if exc.__cause__ is not None:
                      chained_msg = _cause_message
                      chained_exc = exc.__cause__
                  elif (exc.__context__  is not None and
                        not exc.__suppress_context__):
                      chained_msg = _context_message
                      chained_exc = exc.__context__
                  else:
                      chained_msg = None
                      chained_exc = None
  
                  output.append((chained_msg, exc))
                  exc = chained_exc
              else:
                  output.append((None, exc))
                  exc = None
  
          for msg, exc in reversed(output):
              if msg is not None:
                  yield msg
              if exc.stack:
                  yield 'Traceback (most recent call last):\n'
                  yield from exc.stack.format()
              yield from exc.format_exception_only()
  