isinstance(False, int)

Steven D'Aprano steve at REMOVE-THIS-cybersource.com.au
Fri Mar 5 19:07:29 CET 2010


On Fri, 05 Mar 2010 18:14:16 +0100, mk wrote:

>>>> isinstance(False, int)
> True
>  >>>
>  >>> isinstance(True, int)
> True
> 
> Huh?

Yes. Do you have an actual question?


>  >>> issubclass(bool, int)
> True
> 
> Huh?!

Exactly.

Bools are a late-comer to Python. For historical and implementation 
reasons, they are a subclass of int, because it was normal for people to 
use 0 and 1 as boolean flags, and so making False == 0 and True == 1 was 
the least likely to break code.

E.g. back in the day, you would have something like:

{2:None}.has_key(2) -> 1

So folks would do:

print "The key is", ["missing", "present"][d.has_key(key)]

Which still works even now that has_key returns True or False rather than 
1 or 0.


-- 
Steven



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