Surprise: bools are numbers!

While you might have been surprised that int and float aren’t related types, you’ll be even more surprised to learn that bool is closely related to int:

What? A bool is an int? Like the C language before it, Python says that 1 and True are equivalent, and 0 and False are equal. Look:

Observe, however, that True is equal to 1 but is not the same thing as 1:

(Nevermind the warnings: they’re just saying that it doesn’t usually make sense to use is when both sides are literals.)

We can see the relationships between bool and int in another light: every bool is an int, but not the otherway round (e.g., 2 is “truthy”, but it’s not equal to True like 1 is). We say that bool is a subclass or subtype of int. There’s a Python function that helps here:

issubclass(t1, t2)

Returns True when t1 is a subclass of t2; returns False otherwise.