如何模拟"+" python中的运算符(特别是datetime.date + datetime.timedelta) [英] How to mock the "+" operator in python (specifically datetime.date + datetime.timedelta)

问题描述

我在Django中解决了一些日期模拟问题，并且遇到了以下最后一个障碍(我希望).我有一个FakeDate类，它从datetime.date派生而来，它是模拟出来的.

I have working through some date mocking issues in Django, and have the final hurdle (I hope) is the following situation. I have a FakeDate class, which derives from datetime.date, which it mocks out.

FakeDate类按预期工作，但是在向FakeDate添加datetime.timedelta时遇到问题，因为它返回的是真正的datetime.date，而不是模拟对象.这很重要，因为第三方库中的其他地方都有isinstance(value, datetime.date)检查，使用timedelta时该检查总是会失败.

The FakeDate class works as expected, however I get a problem when adding a datetime.timedelta to the FakeDate, in that it returns a genuine datetime.date, rather than the mock. This is important as elsewhere in a third party library there is an isinstance(value, datetime.date) check, which will always fail when using timedelta.

>>> import mock
>>> import datetime
>>>
>>> class FakeDate(datetime.date):
...     @classmethod
...     def today(cls):
...         return cls(1999, 12, 31)
...
>>> FakeDate.today()
FakeDate(1999, 12, 31)
>>> FakeDate(2000, 1, 1)
FakeDate(2000, 1, 1)
>>> FakeDate(1999, 12, 31) + datetime.timedelta(days=1)
datetime.date(2000, 1, 1)

我希望FakeDate + timedelta附加项返回FakeDate对象而不是datetime.date对象-我想这涉及以某种方式修补timedelta-但是如何/在哪里可以做到这一点?

I want the FakeDate + timedelta addition to return a FakeDate object rather than a datetime.date object - which I imagine involves patching the timedelta somehow - but how / where can I do this?

推荐答案

在FakeDate()类中添加__add__方法:

class FakeDate(datetime.date):
     @classmethod
     def today(cls):
         return cls(1999, 12, 31)
     def __add__(self, other):
         res = super(FakeDate, self).__add__(other)
         return type(self)(res.year, res.month, res.day)

演示:

>>> class FakeDate(datetime.date):
...      @classmethod
...      def today(cls):
...          return cls(1999, 12, 31)
...      def __add__(self, other):
...          res = super(FakeDate, self).__add__(other)
...          return type(self)(res.year, res.month, res.day)
... 
>>> FakeDate.today() + datetime.timedelta(days=1)
FakeDate(2000, 1, 1)

请注意，您可以在此处将实际添加的内容简单地委派给datetime.date类.我们要做的就是将结果转换回FakeDate()实例.

Note that you can simply delegate the actual adding to the datetime.date class here; all we need to do is convert the result back to a FakeDate() instance.

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