How many is "too many" with lists?

Neel Krishnaswami neelk at brick.cswv.com
Thu May 4 01:33:02 CEST 2000


Courageous <jkraska1 at san.rr.com> wrote:
> Neel Krishnaswami wrote:
> >
> > [use xrange] 
>
> x = 1000000
> while x > 0
> 	dosomething()
> 	x = x - 1
> 
> That seemed overbearing. So you're saying that
> 
> for x in xrange ( 1000000 )
> 	dosomething()
> 
> is equally unexpensive?

Yes. It has pretty much the same behavior as range() (you just can't
mutate any elements), but doesn't generate a real list, instead
computing the numbers on demand:

    Python 1.5.2 (#8, May 12 1999, 17:46:31)  [GCC 2.7.2.1] on linux2
    Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
    >>> n = 2**30
    >>>
    >>> x = range(n)
    Traceback (innermost last):
      File "<stdin>", line 1, in ?
    MemoryError
    >>>
    >>> y = xrange(n)
    >>> len(y)
    1073741824


Neel



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