問題描述

我需要在測(cè)試中修補(bǔ)當(dāng)前日期時(shí)間.我正在使用這個(gè)解決方案:

I need to patch current datetime in tests. I am using this solution:

def _utcnow():
    return datetime.datetime.utcnow()


def utcnow():
    """A proxy which can be patched in tests.
    """
    # another level of indirection, because some modules import utcnow
    return _utcnow()

然后在我的測(cè)試中，我會(huì)執(zhí)行以下操作:

Then in my tests I do something like:

    with mock.patch('***.utils._utcnow', return_value=***):
        ...

但今天我想到了一個(gè)想法，我可以通過修補(bǔ)函數(shù) utcnow 的 __call__ 來簡化實(shí)現(xiàn)，而不是額外添加一個(gè) _utcnow.

But today an idea came to me, that I could make the implementation simpler by patching __call__ of function utcnow instead of having an additional _utcnow.

這對(duì)我不起作用:

    from ***.utils import utcnow
    with mock.patch.object(utcnow, '__call__', return_value=***):
        ...

如何優(yōu)雅地做到這一點(diǎn)?

How to do this elegantly?

推薦答案

當(dāng)你修補(bǔ)一個(gè)函數(shù)的 __call__ 時(shí)，你是在設(shè)置那個(gè) 的 __call__ 屬性實(shí)例.Python 實(shí)際上調(diào)用了類上定義的 __call__ 方法.

When you patch __call__ of a function, you are setting the __call__ attribute of that instance. Python actually calls the __call__ method defined on the class.

例如:

>>> class A(object):
...     def __call__(self):
...         print 'a'
...
>>> a = A()
>>> a()
a
>>> def b(): print 'b'
...
>>> b()
b
>>> a.__call__ = b
>>> a()
a
>>> a.__call__ = b.__call__
>>> a()
a

將任何東西分配給 a.__call__ 是沒有意義的.

Assigning anything to a.__call__ is pointless.

但是:

>>> A.__call__ = b.__call__
>>> a()
b

TLDR;

a() 不調(diào)用 a.__call__.它調(diào)用 type(a).__call__(a).

TLDR;

a() does not call a.__call__. It calls type(a).__call__(a).

回答為什么type(x).__enter__(x) 而不是 Python 標(biāo)準(zhǔn) contextlib 中的 x.__enter__()?".

There is a good explanation of why that happens in answer to "Why type(x).__enter__(x) instead of x.__enter__() in Python standard contextlib?".

特殊方法查找的 Python 文檔中記錄了此行為.

這篇關(guān)于修補(bǔ)函數(shù)的 __call__的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！