PEP 322: Reverse Iteration (second revision, please comment)

[Paul Moore]

"Raymond Hettinger" <vze4rx4y at verizon.net> writes:

> The key changes are:
>
> * reversed() is being preferred to ireverse() as the best name.

Good. The explanation of why reverse() is not an option helps, too.

> * the sample implementation now clearly shows a check for a custom
>   reverse method and a guard against being applied to a mapping.

I stumbled over this, as using the existence of has_key to reject
mappings seemed odd. Surely even without this check, the sample
implementation would fail on a mapping, with a KeyError at the yield?

> * added sample output for enumerate.__reversed__ to show
>   how a custom reverse method would work

Are you proposing to add such a custom reverse method to enumerate?

> * explained why the function is proposed as a builtin and why attachment
>    to another module or type object is not being considered further.

This was very useful. It may not convince everyone, but it helped me
see your point of view a little better.

> Please continue to contribute your thoughts.  I'm especially interested
> in people examining their own code to verify that the new function
> adds clarity and improves performance.

I don't think I have any real cases where I'd use this. But I agree
with your comments, that this "feels like" a basic looping construct.

> Also, please take a look at the revrange() alternative to see if you
> prefer it or not.

Not really. It feels too much like a special case.

Overall, I'm +0 going on +1 (the main reason I'm not +1 is the fact
that I have no code that would actually *use* this feature at
present...)

Paul,
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