comparing booleans

Duncan Booth me at privacy.net
Thu Jan 29 15:31:33 CET 2004


Dang Griffith <noemail at noemail4u.com> wrote in 
news:eaa90cc908c7a217f0d6475e41c7622d at news.teranews.com:

> Interestingly, and I'm not sure why:
>>>> (True != True) != True
> True
>>>> True != (True != True)
> True
>>>> True != True != True
> False

You can chain comparison operators in Python. e.g.

    a < b < c

is the same as:

    (a < b) && (b < c)

except that if b is an expression the first form evaluates it exactly once 
whereas the second form evaluates it either once or twice.

You can use any comparison operators in this form, so your True!=True!=True 
is just shorthand for:

    (True!=True) && (True!=True)

which is in turn equivalent to:

    False && (True!=True)

and 'False && anything' gives False.



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