[Numpy-discussion] logical priority
Fernando.Perez at colorado.edu
Wed Feb 9 10:24:27 EST 2005
Stephen Walton wrote:
> Fernando Perez wrote a good deal clarifying how Python's logical
> operators work, for which I'm grateful. One brief comment:
>>Bytecode analysis can be really useful to understand this kind of
>>subtle issues. I can't think of any language where this approach is
>>as easy to do and friendly as in python.
> Pardon me, but this sounds a bit like looking at the assembly language
> Fortran generates in order to understand the subtleties of that language
> :-) . I know people who used to do that, and were proud of it, but I'd
Oh, and it is :) It's just that it's so immediate to do it in python, that it
actually becomes a normal approach. I've often used it to clarify behavior or
performance issues to myself. I'm not proud of it, it's just a useful trick
which can come in handy in certain cases.
> rather the language itself didn't behave in surprising ways. At least
> in Fortran, 'a .and. b' only made sense if a and b were both of type
> LOGICAL; in fact, it was a compile time error if they weren't.
You can argue that this is a wart (I don't think it is), but it was certainly
done by design:
'and' is meant to provie truth checking, with (critically important in many
applications) short-circuit behavior. '&' is a binary operation (hence
necessarily non short-circuiting, due to python's argument evaluation rules),
most often used for bitwise manipulations. It seems clear to me that they
both have a valid use.
> Anyway, we've wandered afar from the main point: what is the best way
> to duplicate the functionality of the following MATLAB snippet:
> f = ~isnan(data1) & ~isnan(data2);
I don't have a clean answer for this one, sorry.
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