Last Python 2.7 supported release will be on 2020-01-01 (or before)

[mr-c]

I suggest that whatever the PyPI release of argparse2tool is on 2020-01-01 be the last to include Python 2.7 support.

@erasche If you approve, then I am happy to implement a warning in the codebase and README, etc.. (as was done for cwltool and friends).

[hexylena]

Sounds good to me! :)

[bernt-matthias]

In #65 I enabled py 3.7 for the tests.

[bernt-matthias]

Just thinking about this again. Since there is still quite a bit of python 2.x software out there I'm wondering if we should try to keep 2.x compatibility.

[hexylena]

I have no motivation for it. I'm sure there's value in it.

I jumped the gun on this one, and remove futurize a while back so, we'll need to re-add support for it if you want to do that.