Drop EoLed Python versions (including python 2)

[rooterkyberian]

All python versions older than 3.6 are long dead. https://endoflife.date/python

Motivation for removing them is quite simple - its just easier to support less python versions and python 3.x line has introduced number of nice features that we can start leveraging (fstrings, type hints among others). You can already see some improvements done by pyupgrade in this PR.

Please note just removing them here, thanks to pip support for python_requires will not break old installations assuming they have a setuptools>=24.2.0 and pip>=9.0.0 .

1) document the python versions supported in setup.py 2) update tox, github actions config 3) run pyupgrade --py36-plus 4) remove six package

[codecov[bot]]

Codecov Report

Merging #340 (c5a2c3b) into main (5a17754) will decrease coverage by 0.31%. The diff coverage is 95.74%.

@@            Coverage Diff             @@
##             main     #340      +/-   ##
==========================================
- Coverage   93.80%   93.49%   -0.32%     
==========================================
  Files          33       33              
  Lines        1066     1015      -51     
==========================================
- Hits         1000      949      -51     
  Misses         66       66              

Impacted Files	Coverage Δ
flask_dance/__init__.py	100.00% <ø> (ø)
flask_dance/consumer/oauth1.py	68.60% <ø> (-0.37%)	:arrow_down:
flask_dance/fixtures/pytest.py	91.66% <ø> (-0.34%)	:arrow_down:
flask_dance/contrib/strava.py	95.45% <66.66%> (-0.38%)	:arrow_down:
flask_dance/contrib/reddit.py	96.29% <75.00%> (-0.26%)	:arrow_down:
flask_dance/consumer/base.py	90.00% <100.00%> (-0.25%)	:arrow_down:
flask_dance/consumer/oauth2.py	92.23% <100.00%> (-0.08%)	:arrow_down:
flask_dance/consumer/requests.py	100.00% <100.00%> (ø)
flask_dance/consumer/storage/__init__.py	70.37% <100.00%> (-1.06%)	:arrow_down:
flask_dance/consumer/storage/sqla.py	93.57% <100.00%> (ø)
... and 21 more

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[daenney]

I'm generally fine with this and I agree it makes some stuff easier. I'd like to get the Dropbox one landed and tagged with Python 2 support still in there though. After that we can proceed with this PR and tag a new major version of the library.

@singingwolfboy Do you have any other big things you'd like to do? I don't feel we can drop Python 2 support in a minor release, so now would be an opportunity to do any other changes that might not be backwards compatible.

[singingwolfboy]

I just released v3.3.0, and I think we can make this change for Flask-Dance v4.0.0. This PR is already pretty comprehensive; the only thing I can think of off the top of my head is simplifying all the places where we do this:

try:
    from flask import _app_ctx_stack as stack
except ImportError:
    from flask import _request_ctx_stack as stack

We should be able to just do from flask import _app_ctx_stack -- the except ImportError block is only relevant for very, very old versions of Flask that might not even run on Python 3.

[rooterkyberian]

rebased to current main, removed old flask import

@singingwolfboy is anything else needed here?

[rooterkyberian]

anything else?

[singingwolfboy]

Thanks so much! Just merged it 🎉