Lambda evaluation
Jp Calderone
exarkun at divmod.com
Thu Oct 6 22:27:00 CEST 2005
On Thu, 06 Oct 2005 16:18:15 -0400, Joshua Ginsberg <listspam at flowtheory.net> wrote:
>So this part makes total sense to me:
>
>>>> d = {}
>>>> for x in [1,2,3]:
>... d[x] = lambda y: y*x
>...
>>>> d[1](3)
>9
>
>Because x in the lambda definition isn't evaluated until the lambda is
>executed, at which point x is 3.
>
>Is there a way to specifically hard code into that lambda definition the
>contemporary value of an external variable? In other words, is there a
>way to rewrite the line "d[x] = lambda y: y*x" so that it is always the
>case that d[1](3) = 3?
There are several ways, but this one involves the least additional typing:
>>> d = {}
>>> for x in 1, 2, 3:
... d[x] = lambda y, x=x: y * x
...
>>> d[1](3)
3
Who needs closures, anyway? :)
Jp
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