Hey,

according to PEP 3101, the new string.Formatter class is supposed to replace the old string formatting with %. At least that is what I was always thinking. Given that argparse is a Python 3.2+ exclusive module, I think it should make use of that new formatting method.

Is there any special reason why that is not the case and the old %-formatting is used? It feels a bit weird to have Python 3 code using only string.Formatter and then have a short section where the old formatter is used – especially when that module was introduced with Python 3.2.

Well argparse exists since 2006 (ref [1]), and "should work on Python >= 2.3" (ref [2]).
It was merged in the standard library with Python 3.2.

However, I agree we may switch to the advanced string formatting for this module.


[1] http://objectmix.com/python/180879-%5Bann%5D-argparse-module.html
[2] http://pypi.python.org/pypi/argparse#compatibility

There's no reason to switch the implementation.  The % formatting isn't going away and we've decided against doing switch-overs in existing code (it risks introducing bugs while conferring zero benefits to users).

Thinking about https://bugs.python.org/issue34744, I realized that the new style formatting could provide some added flexibility to the help lines.

I think new style formatting could be added in parallel with the existing style, as an alternative, not as a replacement.

With that option a help line like:

'help for {dest} or {option_strings[0]} default is {default}'  

could be used.