The documentation for a None (empty) format for floats indicates that it is equivalent to the g format. This does not appear to be correct (http://stackoverflow.com/questions/16525924/precise-definition-of-float-string-formatting).

The Python 3.4 documentation (https://docs.python.org/3.4/library/string.html#format-specification-mini-language) seems to be much closer to what Python 2.7 does.

It would be useful to have a more correct documentation for the effect of a None format for floats in Python 2.7 (maybe by copying the Python 3.4 documentation if it applies).