For loops with explicit indices -- again

[Greg Ewing]

Armin Rigo wrote:
> 
>     it = iter(lst)
>     for x in it:
>         if x>0:
>             lst[it.count-1] -= 1

I find this ugly, particularly the need to use count-1
rather than just count. It's just begging for off-by-one
errors.

>     it.count += 1    # skip next element
>     it.count -= 1    # process the same element again
>     it.count = 0    # full rewind
>     it.count -= 1; del lst[it.count]    # remove bad item from list

This is even worse! It's tantamount to modifying
a loop control variable inside the loop, which is
widely regarded as a Bad Thing To Do from a
maintainability standpoint.

If the ability to modify the count is dropped,
I see nothing that can't be achieved more elegantly
using an iterator-wrapper such as the proposed
indexed() function that returns (index, value)
pairs.

-- 
Greg Ewing, Computer Science Dept, University of Canterbury,	  
Christchurch, New Zealand
To get my email address, please visit my web page:	  
http://www.cosc.canterbury.ac.nz/~greg