列出修饰方法的参数

Question

I want to list the arguments of my methods for a self documenting REST API. I have found that I can get the arguments of a method using:

method.__code__.co_varnames[:method.__code__.co_argcount]

However, this does not work when the method is decorated.

class Rator:

    def __init__(self):
        pass

    def __call__(self, func):
        def wrapper(instance, **kwargs):
            func(instance, **kwargs)
        return wrapper


class Klass:

    def method(self, var_one=None, var_two=None):
        pass

    @Rator()
    def decorated_method(self, var_one=None, var_two=None):
        pass


if __name__ == '__main__':
    klass = Klass()
    print("method args is " + str(klass.method.__code__.co_varnames))
    print("decorated method args is " + str(klass.decorated_method.__code__.co_varnames))

Outputs

method args is ('self', 'var_one', 'var_two')
decorated method args is ('instance',)

A solution that does not require change of the decorator is preferred.

I know that this question is a duplicate of How to retrieve method arguments of a decorated python method , but it has since long been dead.

Answer 1

You need wrap you decorator with functools.wraps , then you can can inspect the methods via inspect.signature() :

import inspect
from functools import wraps


class Rator:
    def __init__(self):
        pass

    def __call__(self, func, **kwargs):
        @wraps(func)
        def wrapper(instance):
            func(instance, **kwargs)
        return wrapper


class Klass:
    def method(self, var_one=None, var_two=None):
        pass

    @Rator()
    def decorated_method(self, argument1, var_one=None, var_two=None):
        pass


if __name__ == '__main__':
    klass = Klass()
    print("method args is ", inspect.signature(klass.method))
    print("decorated method args is ", inspect.signature(klass.decorated_method))

Prints:

method args is  (var_one=None, var_two=None)
decorated method args is  (argument1, var_one=None, var_two=None)