"0 in [True,False]" returns True

Steven D'Aprano steve at REMOVETHIScyber.com.au
Tue Dec 13 22:15:28 CET 2005


On Tue, 13 Dec 2005 09:46:30 +0000, Steve Holden wrote:

> Paul Rubin wrote:
>> Steve Holden <steve at holdenweb.com> writes:
>> 
>>>The really interesting question your post raises, though, is "Why do
>>>you feel it's necessary to test to see whether a variable is a
>>>Boolean?".
>> 
>> 
>> What's the point of having Booleans, if you can't tell them from integers?
> 
> Booleans are specifically defined as a subtype of int at the C level. 

That's an implementation detail, and in fact an explicit decision made,
not a inescapable fact of programming. What you are saying is,
effectively, the point of having bools which are subclasses of ints is
that Guido wanted them that way.


> One might also ask "what's the point of having floats if you can't tell 
> them from integers":

But you certainly can:

py> isinstance(True, int)
True
py> isinstance(0.0, int)
False

However, you can also ask:

py> isinstance(True, bool)
True
py> isinstance(1, bool)
False

or even:

py> type(True) == type(1)
False

but, I believe, using type() is frowned upon.



-- 
Steven




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