如何动态更改子类中方法的签名？ [英] How to dynamically change signatures of method in subclass?

问题描述

使用 classmethod 动态更改子类中的方法时，如何动态更改方法的签名？

When using classmethod to dynamic change the method in subclass, how to dynamic change signatures of method?

示例

import inspect

class ModelBase(object):

    @classmethod
    def method_one(cls, *args):
        raise NotImplementedError

    @classmethod
    def method_two(cls, *args):
        return cls.method_one(*args) + 1

class SubClass(ModelBase):
    @staticmethod
    def method_one(a, b):
        return a + b

test = SubClass()

try:
    print(inspect.signature(test.method_two))
except AttributeError:
    print(inspect.getargspec(test.method_two).args)

我要 test.method_two 获取 test.method_one 的签名。如何重写父类 ModelBase ？

I want test.method_two to get the signatures of test.method_one. How to rewrite parent class ModelBase?

我已阅读有关保留装饰功能的签名。在python3.4 +中， functools.wraps 有助于保留修饰函数的签名。我想将其应用于类方法。

I have read about Preserving signatures of decorated functions. In python3.4 +, functools.wraps helps to preserve signatures of decorated functions. I want to apply it to class method.

当使用 functools.wraps 时，我需要分配装饰方法的名称。但是在这种情况下，如何在 classmethod 之外访问修饰方法？

when uses functools.wraps, I need to assign decorated method's name. But how to access decorated method outside classmethod in this situation?

from functools import wraps

class ModelBase(object):

    @classmethod
    def method_one(cls, *args):
        raise NotImplementedError

    @classmethod
    def method_two(cls):
        @wraps(cls.method_one)
        def fun(*args):
            return cls.method_one(*args) + 1
        return fun

method_two 返回包装的函数，但我必须将其与 test.method_two（）（* arg）一起使用。这种方法不是直接的。

method_two returns a wrapped function, but I must use it with test.method_two()(*arg). This method is not directly.

推荐答案

如果这只是出于自省目的，则可以覆盖 __ getattribute __ ModelBase 上的code>，每次访问 method_two 时，我们返回一个具有<$签名的函数c $ c> method_one 。

If this is only for introspection purpose you could override __getattribute__ on ModelBase and every time method_two is accessed we return a function that has the signature of method_one.

import inspect

def copy_signature(frm, to):
    def wrapper(*args, **kwargs):
        return to(*args, **kwargs)
    wrapper.__signature__ = inspect.signature(frm)
    return wrapper


class ModelBase(object):

    @classmethod
    def method_one(cls, *args):
        raise NotImplementedError

    @classmethod
    def method_two(cls, *args):
        return cls.method_one(*args) + 1

    def __getattribute__(self, attr):
        value = object.__getattribute__(self, attr)
        if attr == 'method_two':
            value = copy_signature(frm=self.method_one, to=value)
        return value


class SubClass(ModelBase):
    @staticmethod
    def method_one(a, b):
        return a + b


class SubClass2(ModelBase):
    @staticmethod
    def method_one(a, b, c, *arg):
        return a + b

演示：

>>> test1 = SubClass()
>>> print(inspect.signature(test1.method_two))
(a, b)
>>> test2 = SubClass2()
>>> print(inspect.signature(test2.method_two))
(a, b, c, *arg)

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