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There is a newer version: 4.23.0.17664

This rule raises an issue when operators in and not in are called with a right operand not supporting membership
protocol.
Why is this an issue?
Operators in and not in, also called "membership test operators", require that the right operand
supports the membership protocol.
In order to support the membership protocol, a user-defined class should implement at least one of the following methods:
__contains__, __iter__, __getitem__.
If none of these methods is implemented, a TypeError will be raised when performing a membership test.
How to fix it
Code examples
Noncompliant code example
myint = 42

if 42 in myint:  # Noncompliant: integers don't support membership protocol
    ...

class A:
    def __init__(self, values):
        self._values = values

if "mystring" in A(["mystring"]):  # Noncompliant: class A doesn't support membership protocol
    ...

Compliant solution
mylist = [42]

if 42 in mylist:
    ...

class MyContains:
    def __init__(self, values):
        self._values = values

    def __contains__(self, value):
        return value in self._values

if "mystring" in MyContains(["mystring"]):
    ...

# OR

class MyIterable:
    def __init__(self, values):
        self._values = values

    def __iter__(self):
        return iter(self._values)

if "mystring" in MyIterable(["mystring"]):
    ...

# OR

class MyGetItem:
    def __init__(self, values):
        self._values = values

    def __getitem__(self, key):
        return self._values[key]

if "mystring" in MyGetItem(["mystring"]):
    ...

Resources
Documentation

   Python Documentation - Membership test operations