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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 20:15:24 +0100
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On 02/05/2015 19:34, BartC wrote:
> On 02/05/2015 17:39, Mark Lawrence wrote:
>> On 02/05/2015 17:17, BartC wrote:
>>> On 02/05/2015 16:40, Mark Lawrence wrote:
>
>
>>>> 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?
>>>
>>> Your example is the equivalent of 'forall' in other languages, where you
>>> iterate over the values of some collection of data.
>>>
>>> I agree that most for-loops in Pythonic code probably fall into that
>>> category.
>>>
>>> But for looping over a simple integer range, then using 'range' to
>>> denote the range (and build a list as it used to do), was how it was
>>> done. And earlier on people would have been porting coding code to
>>> Python at which point a straightforward 'for i=a to b' loop suddenly
>>> acquired a substantial overhead it didn't have before!
>>>
>>
>> All you are saying is that they didn't bother reading the docs and
>> learning how to write a *PYTHON* for loop.  Failing that don't bother
>> using range, just directly convert your (say) C loop into Python.  I
>> really don't see any issue here at all.
>
> OK, so it's the programmer's fault if as fundamental a concept as a
> for-loop ranging over integers is implemented inefficiently. He has to
> transform it into high-level terms, or has to reconstruct it somehow
> using a while-loop and an incrementing loop index.
>
> Now I understand (why Python has been beset for so long with performance
> problems, if that is a typical attitude!).
>
> BTW, why did they introduce the 'xrange' thing; for fun? Or did someone
> realise there might have been an issue after all?
>
> (I tried an empty loop counting to 1 billion in Python 2.x, using 'for i
> in range'. It ran out of memory. Counting to 100 million instead, it
> worked, but still used a massive 1.5GB RAM while doing so (and took 6
> seconds to count to 100M, not too bad for Python)
>
> Outside Python, it might typically take a few seconds to count to 1
> billion, and would use virtually no memory.
>
> Why would anyone want to loop over all those numbers instead of
> iterating over actual data? For any number of reasons. Counting how many
> happy numbers are in that range for one!)
>

I give up.

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence