[issue5237] Allow auto-numbered replacement fields in str.format() strings

[Eric Smith]

Eric Smith <eric at trueblade.com> added the comment:

About '{:{fmt}}' and other wacky combinations, like '{.__doc__}':

It's much easier and cleaner in the code to allow these cases than it
would be to disallow them. And I rather like the '{:{fmt}}' example!

I suggest leaving them in. They might be useful, and it makes the
implementation cleaner. I think it will be easier to document, as well.
There are no special cases to describe: If the field name is omitted,
it's auto-numbered with a sequential index number. You can't mix
auto-numbering and manual specification of indexes.

As for string.Formatter, I agree we should leave it alone. I'd be
surprised if anyone is actually using it, anyway. But I'd love to hear
otherwise.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue5237>
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