There is a module that implements this for optparse: <https://hg.furius.ca/public/optcomplete/>; I contacted the author when argparse was moved to the standard library and he told me that he would like to support argparse but had to time to code it.

optcomplete is 451 physical lines long, and 211 single logical lines long (courtesy of the sloccount program).  Maybe it would be smaller after being adapted to argparse, but that’s still a large chunk of code to add, and my feeling is that it would not serve a large enough part of our users.  For example, many people use zsh, which has a wholly different completion system.  I’m also given to understand that some people use Windows.

The decision is Steven’s call, as argparse maintainer, but in my opinion the best course would be to update optcomplete to work with argparse, publish it on PyPI, collect feedback and download statistics, and if it proves solid and widely used, reconsider it for stdlib inclusion.