Diez B. Roggisch
deets at nospam.web.de
Fri Jun 1 14:08:36 CEST 2007
Steve Howell wrote:
> --- Sergey Dorofeev <sergey at fidoman.ru> wrote:
>> > What syntax would you suggest for a lambda
>> enhanced to cover your use
>> > case?
>> > I suppose you will end up with roughly the same
>> number of characters, all
>> > crammed in one line -- or broken into lines at a
>> random position as it
>> > happens with overambitious list comprehensions.
>> Agree, this argument is strong.
> FWIW there's the possibility that even without a
> subexpression syntax, some Python implementations
> would detect the duplication of x*x and optimize that
> for you. It would have to know that x*x had no side
> effects, which I think is a safe assumption even in a
> dynamic language like Python.
Of course it's not. You can create arbitrarily overloaded __mul__-operators
here. Unless you can guarantee that the objects in question are immutable
(which you can only for python-builtins), you can't be sure that there are
no sideeffects. And the needed guarding statements for this kind of
optimization might well eat up the gain from not multiplying two numbers
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