Python 'for' loop is memory inefficient

exarkun at twistedmatrix.com exarkun at twistedmatrix.com
Mon Aug 17 13:40:36 CEST 2009


On 02:12 am, pavlovevidence at gmail.com wrote:
>On Aug 16, 3:35 pm, sturlamolden <sturlamol... at yahoo.no> wrote:
>>On 16 Aug, 14:57, Dennis Lee Bieber <wlfr... at ix.netcom.com> wrote:
>>
>> >         Well, the alternative would be to have two keywords for 
>>looping: one
>> > for your "simple" incrementing integer loop, and another for a loop 
>>that
>> > operates over the elements of some collection type.
>>
>>A compiler could easily recognise a statement like
>>
>>   for i in range(n):
>>
>>as a simple integer loop.
>
>It would be a simple to do if you were writing it for a different
>langauge was a lot less dynamic than Python is.  It'd be quite a
>complex hack to add it to CPython's compiler while maintaing the
>current highly dynamic runtime semantics and backwards compatibility,
>which is a design constraint of Python whether you like it or not.

In your other message, you said this wasn't a legitimate CPython 
complaint.  Here, you say that it would be a "complex hack" to implement 
this in CPython.  "complex hack" has negative connotations in my mind. 
This seems contradictory to me.
>
>And all this complaining about an issue that can be worked around by
>xrange instead of range.  Sheesh.

Sure.  The specific issue of range vs xrange is quite a small one. 
There is a slightly larger one regarding the flexibility (or relative 
lack thereof) of the CPython runtime, though.

Jean-Paul



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