When and Why is bool a Subclass of int in Python?

Why is bool Technically a Subclass of int in Python?

While using Python's memcached library to store a Boolean value, it's initially surprising to observe its return as an integer. A deeper investigation reveals that Python interprets isinstance(val, int) as True for a bool value, implying that bool is somehow a subclass of int.

This peculiar relationship between bool and int has a historical explanation. Before the introduction of the bool type in Python versions 2.2 or 2.3, the standard representation for Boolean values was using the integers 0 (False) and 1 (True).

To ensure compatibility with existing code that relied on this convention, Python implemented the bool type in a way that mirrored the behavior of 0 and 1. This meant not only preserving their truth values but also extending their functionality to support all integral operations.

As a result, Python's bool type essentially "masquerades" as an integer. While it's possible to utilize bool values in numerical contexts, it's not recommended. Similarly, testing equality of a bool and integer for truth value can lead to unexpected behavior.

This historical evolution explains why bool is a subclass of int in Python. It serves as a historical artifact of Python's language expansion and compatibility requirements.

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