code: def cmd(self, argv):
          
          assert isinstance(argv, (list, tuple)), \
                  "'argv' is not a sequence: %r" % argv
          retval = None
          try:
              argv = self.precmd(argv)
              retval = self.onecmd(argv)
              self.postcmd(argv)
          except:
              if not self.cmdexc(argv):
                  raise
              retval = 1
          return retval
docs: Run one command and exit.
  
              "argv" is the arglist for the command to run. argv[0] is the
                  command to run. If argv is an empty list then the
                  'emptyline' handler is run.
  
          Returns the return value from the command handler.