On 2008-08-01, Terry Reedy <[EMAIL PROTECTED]> wrote:
>> Nevertheless, I think this is probably the best example of the
>> enhanced polymorphism of "if x" yet. I'm kind of surprised no one
>> came up with it.)
>
> I think of Python code as 'generic' rather than 'polymorphic'. I am not
> sure if that is a real difference or not, since I am a bit fuzzy on the
> meaning of 'polymorphic' in this context.
>
> The generality of 'if x:' depends on the context. If x is defined as a
> number by doc or previous code (or possibly even by subsequent code),
> then 'if x:' is equivalent to 'if x != 0:'. At this point, it is a
> stylistic argument which to use.
>
> But here is an example where 'if x:' is more generic.
>
> def solve(a,b):
> 'a and b such that b/a exists'
> if a:
> return a/b
> else:
> raise ValueError('a not invertible, cannot solve'
>
> Now suppose we have a matrix class (2x2 for simplicity and realism).
> Its __bool__ (3.0) method implements 'is non-singular'. As written
> above, solve(mat,vec) works (with compatible mat and vec sizes), but it
> would not with 'if a != 0:'.
>
> Of course, the issue goes away by not looking before the leap:
>
> def solve(a,b):
> return a/b
> # let callers deal with exceptions
> or
> try:
> return a/b
> except...
> # raise customized error
Maybe I'm going to be pedantic here, but I fear that your code won't
work with matrices. The problem is that multiplication is not
commutative with matrices. This means that matrices have two divisions a right
and a left division. A far as I know the "/" operator usaly implements
the left division while solving is done by using a right division.
So your code will probably fail when applied to matrices.
--
Antoon Pardon
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