code: def command(self, *args, **kwargs):
          
          def decorator(f):
              cmd = command(*args, **kwargs)(f)
              self.add_command(cmd)
              return cmd
          return decorator
docs: A shortcut decorator for declaring and attaching a command to
          the group.  This takes the same arguments as :func:`command` but
          immediately registers the created command with this instance by
          calling into :meth:`add_command`.