def __call__(self, func: typing.Callable) -> typing.Callable:
funcname = func.__name__
if self._argname not in inspect.signature(func).parameters:
raise ValueError("{} has no argument {}!".format(
funcname, self._argname))
if not hasattr(func, 'glimpse_args'):
func.glimpse_args = {} # type: ignore
elif func.glimpse_args is None: # type: ignore
raise ValueError("@cmdutils.argument got called above (after) "
"@cmdutils.register for {}!".format(funcname))
arginfo = command.ArgInfo(**self._kwargs)
func.glimpse_args[self._argname] = arginfo # type: ignore
return func
