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> Thanks. I think this part is the main reason I see a start argument to
> enumerate as potentially problematic:
>
> """all variants can easily be misread as starting at the nth item in the
> sequence (much like islice() does now): enumerate(3, 'abcdefg') -->
> (3,'d') (4,'e') (5, 'f') (6, 'g')."""
So the ambiguity is that enumerate(it, start=N) could be taken as
skipping the first N items of it rather than adding N to the index it
returns. (And it is my own argument!) I'd like to withdraw this
argument. There are two separate use cases for using enumerate(): one is
to iterate over a sequence and to have a handy index by which to update
the value in the sequence. Another is for 1-based counting, usually when
printing 1-based ordinals (such as line numbers in files, dates in a
month or months in a year, etc.). N-based counting is less common but
still conceivable. However I see no use for skipping items from the
start, and if that use case ever came up, passing a slice to enumerate()
would be the appropriate thing to do. In fact, if you passed in a slice,
you might also want to pass a corresponding start value so the indices
produced match those of the original sequence.
So, I am still in favor of adding a new argument to enumerate().
I'm neutral on the need for a keyword (don't think it would hurt, not
sure how much it matters). I'm strongly against making it an optional
*leading* argument like Raymond proposed; that's a style I just don't
want to promote, range() and the curses module notwithstanding.
> Is the need to use zip(count(3), seq) for the offset index case really
such
> a burden given the associated benefits in keeping the builtin function
> really simple and easy to understand?
Yes, zip(count(3), seq) is too complex for this simple use case. I've
always solved this so far with this less-than-elegant but certainly
simpler idiom (except for users stuck in the tradition of for-loops in
certain older languages :-):
for i, line in enumerat(lines):
 i += 1
 print "%4d. %s" % (i, line)
and variants thereof.