string.Formatter auto-numbering feature was added in 3.4 and not
available in 2.7. Make the documentation unambiguous.
does an index lookup using :func:`__getitem__`.
.. versionchanged:: 2.7
- The positional argument specifiers can be omitted, so ``'{} {}'`` is
- equivalent to ``'{0} {1}'``.
+ The positional argument specifiers can be omitted for :meth:`str.format` and
+ :meth:`unicode.format`, so ``'{} {}'`` is equivalent to ``'{0} {1}'``,
+ ``u'{} {}'`` is equivalent to ``u'{0} {1}'``.
Some simple format string examples::