试图模拟 datetime.date.today()，但不工作

问题描述

谁能告诉我为什么这不起作用?

Can anyone tell me why this isn't working?

>>> import mock
>>> @mock.patch('datetime.date.today')
... def today(cls):
...  return date(2010, 1, 1)
...
>>> from datetime import date
>>> date.today()
datetime.date(2010, 12, 19)

也许有人可以提出更好的方法?

Perhaps someone could suggest a better way?

推荐答案

有几个问题.

首先，您使用 mock.patch 的方式不太正确.当用作装饰器时，它仅在装饰函数内将给定的函数/类(在本例中为 datetime.date.today)替换为 Mock 对象.所以，只有在你的 today() 中，datetime.date.today 才会是一个不同的函数，这似乎不是你想要的.

First of all, the way you're using mock.patch isn't quite right. When used as a decorator, it replaces the given function/class (in this case, datetime.date.today) with a Mock object only within the decorated function. So, only within your today() will datetime.date.today be a different function, which doesn't appear to be what you want.

你真正想要的似乎更像是这样的:

What you really want seems to be more like this:

@mock.patch('datetime.date.today')
def test():
    datetime.date.today.return_value = date(2010, 1, 1)
    print datetime.date.today()

很遗憾，这行不通:

>>> test()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "build/bdist.macosx-10.6-universal/egg/mock.py", line 557, in patched
  File "build/bdist.macosx-10.6-universal/egg/mock.py", line 620, in __enter__
TypeError: can't set attributes of built-in/extension type 'datetime.date'

这会失败，因为 Python 内置类型是不可变的 - 请参阅 这个答案了解更多详情.

This fails because Python built-in types are immutable - see this answer for more details.

在这种情况下，我将自己继承 datetime.date 并创建正确的函数:

In this case, I would subclass datetime.date myself and create the right function:

import datetime
class NewDate(datetime.date):
    @classmethod
    def today(cls):
        return cls(2010, 1, 1)
datetime.date = NewDate

现在你可以这样做了:

>>> datetime.date.today()
NewDate(2010, 1, 1)

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