unsupported-membership-test / E1135

Message emitted:

Value '%s' doesn't support membership test

Description:

Emitted when an instance in membership test expression doesn't implement membership protocol (__contains__/__iter__/__getitem__).

Problematic code:

class Fruit:
    pass


apple = "apple" in Fruit()  # [unsupported-membership-test]

Correct code:

class Fruit:
    FRUITS = ["apple", "orange"]

    def __contains__(self, name):
        return name in self.FRUITS


apple = "apple" in Fruit()

Created by the typecheck checker.