Question

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?

Could you give me an example to demonstrate?

Answer 1

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

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.