code: def do_sticky(self, arg):
          
          if arg:
              try:
                  start, end = map(int, arg.split())
              except ValueError:
                  print('** Error when parsing argument: %s **' % arg,
                        file=self.stdout)
                  return
              self.sticky = True
              self.sticky_ranges[self.curframe] = start, end+1
          else:
              self.sticky = not self.sticky
              self.sticky_range = None
          self._print_if_sticky()
docs: sticky [start end]
  
          Toggle sticky mode. When in sticky mode, it clear the screen
          and longlist the current functions, making the source
          appearing always in the same position. Useful to follow the
          flow control of a function when doing step-by-step execution.
  
          If ``start`` and ``end`` are given, sticky mode is enabled and
          only lines within that range (extremes included) will be
          displayed.