[Biopython] When to drop Python 3.6 support?

[Peter Cock]

Hello all,

We'll probably want to make the Biopython 1.79 release in the next
month or so, which would be before Python 3.9 is officially released.
If it all seems to work, we could add a Python 3.9 wheel for Biopython 1.79
later, otherwise we'd aim to officially support it in our subsequent release.

That would leave us targeting Python 3.6, 3.7, 3.8 and 3.9, which starts
to be a burden for continuous integration testing.

I note that Python 3.6 has now been dropped from NumPy 1.20. It would be
good to start preparing to drop Python 3.6 support in Biopython. According
to https://www.python.org/downloads/ and also PEP494, Python will end
support for Python 3.6 in December 2021, about a year away.

Are there any major platforms (e.g. popular Linux distributions) where the
default is Python 3.6 where our users might be inconvenienced? Personally
I switched to using conda (with conda-forge and bioconda) a while back, and
their default Python is quite up to date - so I don't usually worry about the
system provided Python anymore.

I note that PyPy currently implements Python 3.6.9, but they already have
Python 3.7 support in beta:
https://foss.heptapod.net/pypy/pypy/-/wikis/py3.7%20status

There are a few new features in Python 3.7 which may be of interest,
https://www.python.org/dev/peps/pep-0537/#features-for-3-7 - perhaps
the new Data Classes in particular? Nothing there currently strikes me
as a strong reason to drop Python 3.6 early.

Any thoughts, comments, or use cases for Python 3.6?

Peter