Memory allocation in for loops

[Diez B. Roggisch]

> I mean what I really would like is to have something C++ - like "for 
> (int idx = a; idx < b; i++) { .. }" where no internal vector or 
> something like that is allocated but only a few op's on registers are 
> performed; in the whileloop in python the picture is roughly the same 

Use xrange instead - as it is customary for at least python2.1, if not even earlier.


> behind the scenes I guess.. but what about in the forloop? Is python 
> smart enough not to generate an internal vector as it does usually for 
> lists or do I have to apply some modifications (xrange..)? What happens 
> further if I do the following:
> 
> ## 2.1 ##
> 
> def forloop(a,b,lst):
> 
>     for idx in lst.sort():
>         ## ..
>         ## do something
>         ## ..
> 
> #######
> 
> Is the sorting function called in every iteration just to detect that 
> (after the first sorting) it is useless comming back to the loop or does 
> this happen:
> 
> ## 2.2 ##
> 
> def forloop(a,b,lst):
> 
>     lst.sort()
>     for idx in lst:
>         ## ..
>         ## do something
>         ## ..
> 
> #######

The iterable-expression of a for _ in _: is always only evaluated once.

Diez