在Python中进行方法装饰时传递'self'参数 [英] Passing 'self' parameter during methods decorating in Python

问题描述

我想创建装饰器，以显示将哪些参数传递给函数和方法.我已经写了函数代码，但是方法让我头疼.

I want to create decorator that shows which parameters were passed to function and methods. I have already written the code for functions, but methods are giving me a headaches.

这是按预期工作的函数修饰器:

This is function decorator that works as intended:

from functools import update_wrapper


class _PrintingArguments:
    def __init__(self, function, default_comment, comment_variable):
        self.function = function
        self.comment_variable = comment_variable
        self.default_comment = default_comment
        update_wrapper(wrapped=function, wrapper=self)

    def __call__(self, *args, **kwargs):
        comment = kwargs.pop(self.comment_variable, self.default_comment)
        params_str = [repr(arg) for arg in args] + ["{}={}".format(k, repr(v)) for k, v in kwargs.items()]
        function_call_log = "{}({})".format(self.function.__name__, ", ".join(params_str))
        print("Function execution - '{}'\n\t{}".format(comment, function_call_log))
        function_return = self.function(*args, **kwargs)
        print("\tFunction executed\n")
        return function_return


def function_log(_function=None, default_comment="No comment.", comment_variable="comment"):
    if _function is None:
        def decorator(func):
            return _PrintingArguments(function=func, default_comment=default_comment, comment_variable=comment_variable)
        return decorator
    else:
        return _PrintingArguments(function=_function, default_comment=default_comment, comment_variable=comment_variable)

# example use:
@function_log
def a(*args, **kwargs):
    pass


@function_log(default_comment="Hello World!", comment_variable="comment2")
def b(*args, **kwargs):
    pass


a(0, x=1, y=2)
a(0, x=1, y=2, comment="Custom comment!")

b("a", "b", "c", asd="something")
b("a", "b", "c", asd="something", comment2="Custom comment for b!")

代码执行的输出:

Function execution - 'No comment.'
    a(0, y=2, x=1)
    Function executed

Function execution - 'Custom comment!'
    a(0, y=2, x=1)
    Function executed

Function execution - 'Hello World!'
    b('a', 'b', 'c', asd='something')
    Function executed

Function execution - 'Custom comment for b!'
    b('a', 'b', 'c', asd='something')
    Function executed

我已经为方法尝试了完全相同的装饰器:

I have tried the exactly same decorator for methods:

class A:
    def __init__(self):
        pass

    @function_log
    def method1(self, *args, **kwargs):
        print("\tself = {}".format(self))

    @function_log(default_comment="Something", comment_variable="comment2")
    def method2(self, *args, **kwargs):
        print("\tself = {}".format(self))

a_obj = A()

a_obj.method1(0, 1, p1="abc", p2="xyz")
a_obj.method1(0, 1, p1="abc", p2="xyz", comment="My comment")

a_obj.method2("a", "b", p1="abc", p2="xyz")
a_obj.method2("a", "b", p1="abc", p2="xyz", comment="My comment 2")

输出为:

Function execution - 'No comment.'
    method1(0, 1, p2='xyz', p1='abc')
    self = 0
    Function executed

Function execution - 'My comment'
    method1(0, 1, p2='xyz', p1='abc')
    self = 0
    Function executed

Function execution - 'Something'
    method2('a', 'b', p2='xyz', p1='abc')
    self = a
    Function executed

Function execution - 'Something'
    method2('a', 'b', comment='My comment 2', p2='xyz', p1='abc')
    self = a
    Function executed

我的装饰器未将参数"self"传递给该方法.
我想编写第二个修饰符'method_log'，其作用与'function_log'非常相似. 对于代码:

Parameter 'self' is not passed by my decorator to the method.
I want to write second decorator 'method_log' that would work pretty similar as 'function_log'. For code:

class A:
    def __init__(self):
        pass

    @method_log
    def method1(self, *args, **kwargs):
        print("\tself = {}".format(self))

    @fmethod_log(default_comment="Something", comment_variable="comment2")
    def method2(self, *args, **kwargs):
        print("\tself = {}".format(self))

a_obj = A()

a_obj.method1(0, 1, p1="abc", p2="xyz")
a_obj.method1(0, 1, p1="abc", p2="xyz", comment="My comment")

a_obj.method2("a", "b", p1="abc", p2="xyz")
a_obj.method2("a", "b", p1="abc", p2="xyz", comment="My comment 2")

我想要输出:

Method execution - 'No comment.'
    method1(<__main__.A instance at ...>, 0, 1, p2='xyz', p1='abc')
    self = <__main__.A instance at ...> #
    Function executed

Method execution - 'My comment'
    method1(<__main__.A instance at ...>, 0, 1, p2='xyz', p1='abc')
    self = <__main__.A instance at ...>
    Function executed

Method execution - 'Something'
    method2(<__main__.A instance at ...>, 'a', 'b', p2='xyz', p1='abc')
    self = <__main__.A instance at ...>
    Function executed

Method execution - 'Something'
    method2(<__main__.A instance at ...>, 'a', 'b', comment='My comment 2', p2='xyz', p1='abc')
    self = <__main__.A instance at ...>
    Function executed

推荐答案

由于类在Python中的工作方式，它不适用于您当前的设计.

It's not working with you current design because of how classes work in Python.

实例化一个类时，其上的函数将绑定到实例- 它们成为绑定方法，因此self被自动传递.

When a class is instantiated, the functions on it get bound to the instance - they become bound methods, so that self is automatically passed.

您可以看到它发生了:

class A:
    def method1(self):
        pass

>>> A.method1
<function A.method1 at 0x7f303298ef28>
>>> a_instance = A()
>>> a_instance.method1
<bound method A.method1 of <__main__.A object at 0x7f303a36c518>>

实例化A时，method1从a神奇地转化 function转换为bound method.

When A is instantiated, method1 is magically transformed from a function into a bound method.

您的装饰器替换了method1-而不是实函数， 现在它是_PrintingArguments的实例.魔术 将函数转换为绑定方法的方法不适用于随机方法 对象，即使它们定义了__call__以便它们的行为也像函数一样. (但是，如果您的类实现了Descriptor协议，则可以应用魔术 ，请参见ShadowRanger的答案！).

Your decorator replaces method1 - instead of a real function, it is now an instance of _PrintingArguments. The magic that turns functions into bound methods is not applied to random objects, even if they define __call__ so that they behave like a function. (But that magic can be applied, if your class implements the Descriptor protocol, see ShadowRanger's answer!).

class Decorator:
    def __init__(self, func):
        self.func = func

    def __call__(self, *args, **kwargs):
        return self.func(*args, **kwargs)


class A:
    @Decorator
    def method1(self):
        pass

>>> A.method1
<__main__.Decorator object at 0x7f303a36cbe0>
>>> a_instance = A()
>>> a_instance.method1
<__main__.Decorator object at 0x7f303a36cbe0>

没有魔术. A实例上的method1不是绑定方法， 它只是带有__call__方法的随机对象，不会 self自动通过.

There is no magic. method1 on the instance of A is not a bound method, it's just a random object with a __call__ method, which will not have self passed automatically.

如果要修饰方法，则必须替换修饰的函数 带有另一个实函数，使用__call__的任意对象都不会.

If you want to decorate methods you have to replace the decorated function with another real function, an arbitrary object with __call__ will not do.

您可以修改当前代码以返回实函数:

You could adapt your current code to return a real function:

import functools

class _PrintingArguments:
    def __init__(self, default_comment, comment_variable):
        self.comment_variable = comment_variable
        self.default_comment = default_comment

    def __call__(self, function):
        @functools.wraps(function)
        def decorated(*args, **kwargs):
            comment = kwargs.pop(self.comment_variable, self.default_comment)
            params_str = [repr(arg) for arg in args] + ["{}={}".format(k, repr(v)) for k, v in kwargs.items()]
            function_call_log = "{}({})".format(function.__name__, ", ".join(params_str))
            print("Function execution - '{}'\n\t{}".format(comment, function_call_log))
            function_return = function(*args, **kwargs)
            print("\tFunction executed\n")
            return function_return
        return decorated

def function_log(_function=None, default_comment="No comment.", comment_variable="comment"):
    decorator = _PrintingArguments(
        default_comment=default_comment,
        comment_variable=comment_variable,
    )
    if _function is None:
        return decorator
    else:
        return decorator(_function)

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