Why is Bool a Subclass of Int in Python?

Why is Bool a Subclass of Int in Python?

When interacting with memcached through python-memcached, a bool value is returned as an integer. This surprising observation prompted further investigation.

Understanding the Underlying Logic

In Python, isinstance(True, int) and issubclass(bool, int) both evaluate to True, indicating that bool is a subclass of int. This raises the question: why is this the case?

Historical Context

The introduction of the bool type in Python aimed to enhance the representation of truth values. However, to ensure backward compatibility, the bool type needed to behave identically to 0 and 1 (the previous truth value representations). This extended beyond truth value to encompass all integral operations.

Balancing Compatibility and Evolution

To avoid disrupting existing code that relied on boolean values in non-ideal ways, the bool type was implemented as True and False masquerading as 1 and 0, respectively. This historical decision created the unusual inheritance relationship between bool and int.

Conclusion

The subclass relationship between bool and int is a relic of Python's linguistic evolution. It allows for seamless integration with legacy code that treats boolean values as integers while accommodating the modern usage of the bool type.

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