code: def argument(*param_decls, **attrs):
      
      def decorator(f):
          ArgumentClass = attrs.pop('cls', Argument)
          _param_memo(f, ArgumentClass(param_decls, **attrs))
          return f
      return decorator
docs: Attaches an argument to the command.  All positional arguments are
      passed as parameter declarations to :class:`Argument`; all keyword
      arguments are forwarded unchanged (except ``cls``).
      This is equivalent to creating an :class:`Argument` instance manually
      and attaching it to the :attr:`Command.params` list.
  
      :param cls: the argument class to instantiate.  This defaults to
                  :class:`Argument`.