In Python, a mixin class is a class that is not intended to be used directly, but instead “mixed in” to other classes through multiple inheritance. Mixins are not really a language feature but more of a conventional pattern allowed by Python’s multiple inheritance rules. Unfortunately, adding type hints to mixin classes can be tricky because they implicitly require subclasses to fit a certain shape.

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Adam Johnson

Mixin classes in Python allow additional functionality to be combined into other classes without being used directly, enabled by multiple inheritance. Implementing type hints for mixins is challenging as they require specific subclass shapes. To handle this, mixins can be declared as subclasses of a base class or using protocols for attributes, ensuring type checkers correctly validate the code.

Python type hints: mixin classes