why I don't like range/xrange

[Chris Mellon]

On 16 Feb 2007 07:30:15 -0800, stdazi <stdazi at gmail.com> wrote:
> Hello!
>
> Many times I was suggested to use xrange and range instead of the
> while constructs, and indeed, they are quite more elegant - but, after
> calculating the overhead (and losen flexibility) when working with
> range/xrange, and while loops, you get to the conclusion that it isn't
> really worth using range/xrange loops.
>
> I'd like to show some examples and I'll be glad if someone can suggest
> some other fixes than while a loop :-)
>
> a) range overfllow :
>
>
> for i in range(0, 1 << len(S)) :
> .....
> OverflowError: range() result has too many items
>
> ok, so we fix this one with xrange !
>
> b) xrange long int overflow :
>
> for i in xrange(0, 1 << len(S)) :
> ........
> OverflowError: long int too large to convert to int
>

xrange should be able to handle this. It's probably worth a bug report.

> Next thing I miss is the flexibility as in C for loops :
>
> for (i = 0; some_function() /* or other condition */ ; i++)
>

You'd use a regular for or a while loop here, without the loop index.

> or,
>
> for (i = 0 ; i < 10 ; i++)
>    i = 10;
>

This doesn't do anything as written. For all reasonable uses of it,
you can do it the same way in Python. Writing C code in Python is a
waste of time and an exercise in frustration.

>
> I don't think range/xrange sucks, but I really think there should be
> some other constructs to improve the looping flexibility. Other thing
> may be, that I just miss an equally elegant alternative that's why I'd
> like to hear some suggestions on how to fix the above issues.. (btw,
> I've already browsed the archives related to my issue,but i don't see
> any good solution)
>

Enumeration over range() and xrange() is rare in Python. loops like:

data = [...]
for ii in xrange(len(data)):
   datum = data[ii]

are a wart. Enumerate over whatever you're going to work with.

In some cases, you want the index and the item. Use enumerate for that:

for index, datum in enumerate(data):
    ....