On 7/9/07, Alan G Isaac <[EMAIL PROTECTED]> wrote:
On Mon, 9 Jul 2007, Timothy Hochberg apparently wrote:
> Why not simply use & and | instead of + and *?
A couple reasons, none determinative.
1. numpy is right a Python is wrong it this case
I don't think I agree with this. Once you've decided to make Boolean a
subclass of Int, then Python's behavior seems to be the most sensible. One
could argue (and people did) about whether that was a good choice, but it's
useful for a lot of practical applications. In any event, given that Boolean
subclasses Int, I think the current behavior is probably for the best.
(but granted, I would usually go with Python is such cases)
2. consistency with Boolean matrices
OK. I sort of read past the fact that you were referring to matrices not
arrays. This doesn't matter to me personally because I don't use the matrix
class. I do do matrix algebra on occasion, but the matrix class has never
been helpful for me. YMMV.
Elaboration on 2:
Boolean matrices currently behave as expected, with standard
notation. Related to this, they handle exponents correctly.
Suppose arrays are changed as you suggest.
Then either
- array behavior and matrix behavior are decoupled, or
- matrix behavior is completely broken for boolen matrices
Alan Isaac
PS Examples of good behavior:
>>> x
matrix([[True, True],
[True, False]], dtype=bool)
>>> y
matrix([[False, True],
[True, False]], dtype=bool)
>>> x*y
matrix([[True, True],
[False, True]], dtype=bool)
>>> x**2
matrix([[True, True],
[True, True]], dtype=bool)
x*y and x**2 are already decoupled for arrays and matrices. What if x*y was
simply defined to do a boolean matrix multiply when the arguments are
boolean matrices?
I don't care about this that much though, so I'll let it drop.
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