[Numpy-discussion] Numpy and PEP 343
Paul F. Dubois
paul at pfdubois.com
Tue Feb 28 17:20:16 CST 2006
You're reinventing C++ expression templates, although since Python is
dynamically typed you don't need templates. The crucial feature in C++
that lets it all work is that you can override the action for assignment.
a = b*c + d*e
If we could realize we were at the "equals" sign we could evaluate the
RHS, and assign it to a.
This is not possible in Python; to make is possible would require
slowing down regular assignment, which is perhaps a definition of bad.
a[...] = RHS
could be overridden but it is ugly and 'naive' users will forget.
a := RHS
could be added to the language with the semantics that it tries to do
a.__assignment__(RHS) but Guido told me no long ago. (:->. Also, you
might forget the : in :=.
a.assign(RHS)
would also work but then the original statement would produce a strange
object with surprising results.
David M. Cooke wrote:
> Tim Hochberg <tim.hochberg at cox.net> writes:
>
>> <pie-in-the-sky>
>>
>> An idea that has popped up from time to time is delaying evalution of
>> a complicated expressions so that the result can be computed more
>> efficiently. For instance, the matrix expression:
>>
>> a = b*c + d*e
>>
>> results in the creation of two, potentially large, temporary matrices
>> and also does a couple of extra loops at the C level than the
>> equivalent expression implemented in C would.
>>
>> The general idea has been to construct some sort of psuedo-object,
>> when the numerical operations are indicated, then do the actual
<snip>
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