Force python 3 detection

[patrickfuchs]

I realized that when installing MDAnalysis with python2.7, buildH doesn't issue any error but when it runs, it generates wrong results. So we should add a detection of python 3.7 (or higher).

[patrickfuchs]

Done in 6bc8c68! Question to @HubLot and @pierrepo, in this line I use the Exception UserWarning. Do you think it is the most appropriate?

[pierrepo]

UserWarning seems OK to me.
But i'll advise to check strickly for Python >= 3.6 since f-string are a really nice feature.

[HubLot]

Seems good to me too.
But do you have a reason to restrict to Python >= 3.7 (or even 3.6) ? 3.5 is still maintained for a year for example (https://devguide.python.org/#branchstatus)

By the way, @patrickfuchs you removed the '#' in the first line of the script so it doesn't work anymore :D :

buildH/buildH_calcOP.py

Line 1 in 6bc8c68

!/usr/bin/env python3

[patrickfuchs]

Thanks guys for your answer 😄 ! For the version, it looks like 3.6 could be a good compromise, this could allow us to use f-strings indeed. Thanks also @HubLot for reporting the mistake on line 1, I was too tired yeasterday evening 😉.

[pierrepo]

It looks like the detection of the Python version is not present in the code anymore.

In addition, by using a Python package, setup.cfg enforces Python >= 3.6

We could close this issue.