[Python-Dev] Re: ANN: PEP 335: Overloadable Boolean Operators

[Perry Greenfield]

Tim Hochberg wrote:
> Phillip J. Eby wrote:
>
> [CHOP]
> >
> > As for the numeric use cases, I'm not at all clear why &, |, and ~ 
> (or
> > special methods/functions) aren't suitable.
>
> They often are, but sometimes you want a logical and/or/not and &/|/~
> are mapped to bitwise and/or/not, which isn't always what you want.
> Presumably, if Gregs proposal were adopted, and/or/not would get mapped
> to numarray.logical_and/or/not.
>
I'll go further than that. *Most* of the time Numeric/numarray users
want logical and/or/not. Bitwise operations are, by comparison, rarely
desired.

It is true that one can use the bitwise operators in place of the
logical ones (and currently, that's what I tell people to use), but
you better make sure the arguments are booleans or limited to 0/1 values
or the result is not what is expected. In the great majority of cases
the arguments are booleans, but there are times when that isn't true,
and using the bitwise operators causes real grief if the user has
become accustomed to using the bitwise operator mindlessly.

Furthermore, most new array users naturally expect and/or/not to 
operate on
the array and are usually very annoyed that it doesn't work. This is one
of the largest (if not the largest) remaining warts for using arrays
with Python. I sure would like to see the PEP accepted. No one who
has tried to write many array expressions with the functional or method
equivalents would argue for their use in place of the operators.

Perry Greenfield