code: def error(self, message):
          
          self.print_usage(_sys.stderr)
          self.exit(2, _('%s: error: %s\n') % (self.prog, message))
docs: error(message: string)
  
          Prints a usage message incorporating the message to stderr and
          exits.
  
          If you override this in a subclass, it should not return -- it
          should either exit or raise an exception.