code: def do_until(self, arg):
          
          if arg:
              try:
                  lineno = int(arg)
              except ValueError:
                  self.error('Error in argument: %r' % arg)
                  return
              if lineno <= self.curframe.f_lineno:
                  self.error('"until" line number is smaller than current '
                             'line number')
                  return
          else:
              lineno = None
          self.set_until(self.curframe, lineno)
          self.set_sigint_handler()
          return 1
docs: unt(il) [lineno]
          Without argument, continue execution until the line with a
          number greater than the current one is reached.  With a line
          number, continue execution until a line with a number greater
          or equal to that is reached.  In both cases, also stop when
          the current frame returns.