Why is bool a subclass of int?

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From a comment on http://www.peterbe.com/plog/bool-is-int

It is perfectly logical, if you were around when the bool type was
added to python (sometime around 2.2 or 2.3).

Prior to introduction of an actual bool type, 0 and 1 were the
official representation for truth value, similar to C89. To avoid
unnecessarily breaking non-ideal but working code, the new bool type
needed to work just like 0 and 1. This goes beyond merely truth value,
but all integral operations. No one would recommend using a boolean
result in a numeric context, nor would most people recommend testing
equality to determine truth value, no one wanted to find out the hard
way just how much existing code is that way. Thus the decision to make
True and False masquerade as 1 and 0, respectively. This is merely a
historical artifact of the linguistic evolution.

Credit goes to dman13 for this nice explanation.

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