Steven D'Aprano wrote:
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.
Despite there are good reasons for bool to be int, the newcomer 'wtf'
reaction at first glance is legitimate.
Starting python from scratch, booleans would have not been a subclass of
int (just guessing though), 'cause it makes no sense from a design POV.
Booleans are not ints, 0 does not *mean* False and veracity is not
quantification.
JM
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