Python列表类__contains__方法功能 [英] Python List Class __contains__ Method Functionality

问题描述

__是否包含list类的__ 方法检查对象本身是否是列表的元素，还是检查列表是否包含与给定参数？

Does the __contains__ method of a list class check whether an object itself is an element of a list, or does it check whether the list contains an element equivalent to the given parameter?

您可以举个例子来演示吗？

Could you give me an example to demonstrate?

推荐答案

>>> a = [[]]
>>> b = []
>>> b in a
True
>>> b is a[0]
False

这证明它是一个值检查至少默认），而不是身份检查。请记住，如果需要，可以覆盖 __ contains __（）以使其成为身份检查。但是，默认情况下，不会。

This proves that it is a value check (by default at least), not an identity check. Keep in mind though that a class can if desired override __contains__() to make it an identity check. But again, by default, no.

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