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To: python-list@python.org
From: Mark Lawrence <breamoreboy@yahoo.co.uk>
Subject: Re: l = range(int(1E9))
Date: Sat, 02 May 2015 16:40:44 +0100
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On 02/05/2015 16:26, BartC wrote:
> On 30/04/2015 18:20, Ben Finney wrote:
>> Jon Ribbens <jon+usenet@unequivocal.co.uk> writes:
>
>>> If you use xrange() instead of range() then you will get an iterator
>>> which will return each of the numbers in turn without any need to
>>> create an enormous list of all of them.
>>
>> If you use Python 3 instead of the obsolescent Python 2, the ‘range’
>> callable has this sensible behaviour by default.
>
> When I first looked at Python 20 or so years ago this seemed to be the
> standard way of writing a for-loop:
>
> for i in range(N):
>     ....
>
> I remember being completely astonished at the time that 'range' actually
> created a list of values from 0 to N-1.
>
> Python was already known to be slow yet it deliberately crippled itself
> by using just about the slowest method imaginable of executing a simple
> iterative loop? By first creating a list of a million objects!
>
> And sometimes you weren't even interested in the values but just wanted
> to execute something N times so it was a wasted effort.
>
> That was eventually fixed with xrange, but why do it like that in the
> first place?
>
> (At the time, I was creating bytecode languages as part of the
> applications I was writing. An empty for-loop executed just one bytecode
> per iteration, and it was also the fastest bytecode instruction. An
> empty for-loop executed three Python bytecodes per iteration last time I
> looked. It seems that Python used to like making a rod for its own back.)
>

I first started maybe 14 years ago and the standard way of writing a for 
loop was, and still is:-

for item in items:

When did this change, or has it always been this way and you were simply 
using an idiom from other languages?

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence