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Wed Nov 5 12:06:13 EST 2003 · https://mail.python.org/pipermail/python-dev/2003-November/040015.html

At 05:34 PM 11/5/03 +0100, Samuele Pedroni wrote:
>At 17:09 05.11.2003 +0100, Alex Martelli wrote:
>>On Wednesday 05 November 2003 03:54 pm, Phillip J. Eby wrote:
>>    ...
>> > >reverse iteration.  The iterator object has no way of knowing in advance
>> > >that it is going to be called by reversed().
>> >
>> > Why not change enumerate() to return an iterable, rather than an
>> > iterator?  Then its __reversed__ method could attempt to delegate to the
>> > underlying iterable.  Is it likely that anyone relies on enumerate() being
>> > an iterator, rather than an iterable?
>
>I think he was wondering whether people rely on
>
>
>enumerate([1,2]).next
>i = enumerate([1,2])
>i is iter(i)
>
>working , vs. needing iter(enumerate([1,2]).next

Yes, precisely.

>I think he was proposing to implement enumerate as
>
>class enumerate(object):
>   def __init__(self,iterable):
>     self.iterable = iterable
>
>   def __iter__(self):
>     i = 0
>     for x in self.iterable:
>       yield i,x
>       i += 1
>
>   def __reversed__(self):
>     rev = reversed(self.iterable)
>     try:
>       i = len(self.iterable)-1
>     except (TypeError,AttributeError):
>       i = -1
>     for x in rev:
>        yield i,x
>        i -= 1

Yes, except I hadn't thought it out in quite that much detail.  Thanks for 
the clarification.

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Showing content from https://mail.python.org/pipermail/python-dev/2003-November/040015.html below:

[Python-Dev] Re: PEP 322: Reverse Iteration