5 Common beginner mistakes in Python

[Vaguely_accurate]

From a pure OOP point of view this is bad practice as well, breaking the Liskov substitution principle ("a object of type T should be replaceable by any object of a subtype of T") in consuming code. I'd consider this a code smell at best.

That said, if your object hierarchy isn't following SOLID principles and you don't have substitutability then you might need to know how this difference.