[Numpy-discussion] Truth value of an array

Robert Kern robert.kern@gmail....
Fri Apr 18 15:39:04 CDT 2008


On Fri, Apr 18, 2008 at 3:33 PM, Joe Harrington <jh@physics.ucf.edu> wrote:
> For that matter, is there a reason logical operations don't work on
>  arrays other than booleans?  What about:

The keywords "and", "or", and "not" only work on bool objects; Python
tries to convert the operands using bool(). bool(some_array) raises
the exception just as we've been discussing.

>  Here, both x and y are completely True, but you can't trivially do a
>  logical AND, and the bitwise & isn't the one you want.  You have to
>  cast to boolean manually and do the logical instead.
>
>  Can this be fixed or is there a reason for the exception?

No, it cannot be fixed. Python does not give us a way to overload the
behavior of these keywords.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
 -- Umberto Eco


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