enumerate improvement proposal

James Stroud jstroud at mbi.ucla.edu
Sun Oct 29 12:41:36 CET 2006


James Stroud wrote:
> I think that it would be handy for enumerate to behave as such:
> 
> def enumerate(itrbl, start=0, step=1):
>   i = start
>   for it in itrbl:
>     yield (i, it)
>     i += step
> 
> This allows much more flexibility than in the current enumerate, 
> tightens up code in many cases, and seems that it would break no 
> existing code. Yes, I have needed this behavior with enumerate, like 
> tonight and the current example. I put the "step" parameter in for 
> conceptual symmetry with slicing.
> 
> Here is a case use (or is it use case?):
> 
> 
> # with the proposed enumerate
> import operator
> def in_interval(test, bounds, first=1, reverse=False):
>   op = operator.gt if reverse else operator.lt   # python 2.5
>   bounds = sorted(bounds, reverse=reverse)
>   for i, bound in enumerate(bounds, first):
>     if op(test, bound):
>       return i
>   return i + 1
> 
> 
> # with the existing enumerate
> import operator
> def in_interval(test, bounds, first=1, reverse=False):
>   op = operator.gt if reverse else operator.lt   # python 2.5
>   bounds = sorted(bounds, reverse=reverse)
>   for i, bound in enumerate(bounds):
>     if op(test, bound):
>       return i + first
>   return i + first + 1
> 
> 
> py> # eg
> ...
> py> in_interval(8, bounds)
> 2
> py> in_interval(1, bounds)
> 1
> py> in_interval(1, bounds, reverse=True)
> 5
> py> in_interval(8, bounds, reverse=True)
> 4
> py> in_interval(20, bounds, reverse=True)
> 2
> 
> Of course, I haven't used step here. Even in this trivial example the 
> proposed enumerate cleans the code and logic, eliminating a couple of 
> plus signs. For this real-world example, the practical requirement for 
> reversing the bins obfuscates somewhat the de-obfuscation provided by 
> the proposed enumerate. But I think that it might be obvious that the 
> proposed enumerate could help significantly in cases a bit more 
> complicated than this one.
> 
> Any thoughts?
> 
> James

After a brief reflection, I realized that I just described a 
"for-to-step-do" style loop one might find in many other languages, most 
notably BASIC.

James



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