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If a class implements both ‘__eq__’ and ‘__hash__’, it's important for those implementations to be consistent with each other:
a == b ⇔ hash(a) == hash(b)
TIL that Python will try to help you adhere to this constraint in the presence of subclasses. If you define a subclass, and implement ‘__eq__’ _but not_ ‘__hash__’, then Python will implicitly set ‘__hash__’ to ‘None’ in that class. That way you can't accidentally override the meaning of “equals” in a way that breaks hashability.
‘object.__hash__’ documentation
This has some ramifications with the type system: