code: def _stack_format (stack):
      
      s = StringIO()
      s.write('Traceback:')
      s.write(os.linesep)
      for frame, fname, lineno, method, lines, dummy in reversed(stack):
          s.write('  File %r, line %d, in %s' % (fname, lineno, method))
          s.write(os.linesep)
          s.write('    %s' % lines[0].lstrip())
          if PRINT_LOCALVARS:
              for key, value in frame.f_locals.items():
                  s.write("      %s = " % key)
                  # be careful not to cause a new error in the error output
                  try:
                      s.write(repr(value))
                      s.write(os.linesep)
                  except Exception:
                      s.write("error in repr() call%s" % os.linesep)
      return s.getvalue()
docs: Format a stack trace to a message.
  
      @return: formatted stack message
      @rtype: string