装饰方法：AttributeError: 'function' object has no attribute '__self__'？

Question

我正在处理以asyncio特定的相对时间间隔调用的调度方法。我决定将调度集中到我编写的类的一种方法中，以减少我的项目逻辑出错的机会。

每次计划方法完成时都应调用此类方法。我虽然在loop.call_soon每个方法的末尾添加，但我决定试一试装饰器。

我写了一个类装饰器，然后将它应用于我的主类的一些方法，编写其余的逻辑等等。但是当我尝试在我的项目上测试我的更改时，我得到了一个例外：

AttributeError: 'function' object has no attribute '__self__'

不知何故，装饰我的方法使它成为一个功能。这是我无法理解的事情，为什么会发生这种情况？如何在不放弃装饰器的情况下解决这个问题？

这是我正在尝试做的一个最小、完整且可验证的示例：

import asyncio
from datetime import datetime


class thinkagain:
    loop = asyncio.get_event_loop()

    def __init__(self, f):
        self.fun = f
        self.class_ = f.__self__

    def __call__(self):
        self.fun(*args, **kwords)
        # everything in Python is an object
        setattr(self.fun, "called", datetime.utcnow())
        self.loop.call_later(self.class_.think, 5 * 60)


class DoSomething:
    loop = asyncio.get_event_loop()

    @thinkagain
    def think(self):
        attr = getattr(self.dosomething, "called")
        if attr:
            elapsed = attr - datetime.utcnow()
            seconds = elapsed.seconds
        else:
            seconds = 99999

        if seconds >= 20 * 60:
            self.loop.call_soon(self.dosomething)

    @thinkagain
    def dosomething(self):
        print("I did something awesome!")

loop = asyncio.get_event_loop()
something = DoSomething()
loop.call_soon(something.think)
loop.run_forever()

这是我得到的例外：

Python 3.5.1 (default, Dec  7 2015, 13:41:59) 
[GCC 5.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/tmp/mcve.py", line 19, in <module>
    class DoSomething:
  File "/tmp/mcve.py", line 22, in DoSomething
    @thinkagain
  File "/tmp/mcve.py", line 10, in __init__
    self.class_ = f.__self__
AttributeError: 'function' object has no attribute '__self__'
>>> 

Answer 1

关于装饰器，Graham Dumpleton发表了精彩的演讲 《创建装饰器的高级方法》，讨论了各种装饰风格和技术的内部实现。强烈推荐。

他最后介绍的相关模块：https : //github.com/GrahamDumpleton/wrapt

尽管如此，我用两个版本修改了您的示例。下面的版本按照您的意图将属性直接存储在方法中。

from datetime import datetime

class thinkagain:

    def __init__(self, f):
        # Plain function as argument to be decorated
        self.func = f

    def __get__(self, instance, owner):
        self.instance_ = instance
        return self.__call__

    def __call__(self, *args, **kwargs):
        """Invoked on every call of any decorated method"""

        # set attribute directly within bound method
        bound_method = getattr(self.instance_, self.func.__name__)
        bound_method.__dict__['called'] = datetime.utcnow()

        # returning original function with class' instance as self
        return self.func(self.instance_, *args, **kwargs)


class DoSomething_A:

    @thinkagain
    def think(self, *args, **kwargs):
        print('\n%s' % locals())
        print(self.think.called, args, kwargs)
        self.dosomething()

    @thinkagain
    def dosomething(self):
        print('%s\n' % ('-'*30), locals())
        print("%s I did something awful" % self.dosomething.called)

第二个版本看起来更简洁，它跳过在方法中存储属性并直接在实例中分配它们。

from datetime import datetime

class thinkagain:

    def __init__(self, f):
        # Plain function as argument to be decorated
        self.func = f

    def __get__(self, instance, owner):
        self.instance_ = instance
        return self.__call__

    def __call__(self, *args, **kwargs):
        """Invoked on every call of decorated method"""

        # set attribute on instance
        name = '%s_called' % self.func.__name__
        setattr(self.instance_, name, datetime.utcnow())

        # returning original function with class' instance as self
        return self.func(self.instance_, *args, **kwargs)


class DoSomething_B:

    @thinkagain
    def think(self, *args, **kwargs):
        print('\n%s' % locals())
        print(self.think_called)
        self.dosomething()

    @thinkagain
    def dosomething(self):
        print('%s\n' % ('-'*30), locals())
        print(self.dosomething_called)

两者都会产生相同的期望行为：

>>> something = DoSomething_A().think(1, 2)
{'args': (1, 2), 'kwargs': {}, 'self': <__main__.DoSomething_A object at     0x10209f128>}
2015-12-26 04:13:25.629887 (1, 2) {}
------------------------------
{'self': <__main__.DoSomething_A object at 0x10209f128>}
2015-12-26 04:13:25.647476 I did something awful

和

>>> something = DoSomething_B().think('arg_a', 'arg_b')
{'args': ('arg_a', 'arg_b'), 'kwargs': {}, 'self': <__main__.DoSomething_B object at 0x10209f208>}
2015-12-26 04:13:25.648039
------------------------------
{'self': <__main__.DoSomething_B object at 0x10209f208>}
2015-12-26 04:13:25.648390