Drop Python 3.7 support

[kloczek]

According to https://endoflife.date/python 3.7 has been EOSed almost year ag. Filter all code over pyupgrade --py38-plus.

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[kloczek]

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[pquentin]

buildkite test this please

[pquentin]

@miguelgrinberg In my experience running pyupgrade and making various code changes as part of dropping a Python version is pretty common. For example, in urllib3:

• https://github.com/urllib3/urllib3/pull/1429
• https://github.com/urllib3/urllib3/pull/2044
• https://github.com/urllib3/urllib3/pull/2336
• https://github.com/urllib3/urllib3/pull/3143

Admittedly, some of the changes here are not only related to Python 3.7, so I can open a pull request to run pyupgrade --py37-plus before merging this if you prefer.

[miguelgrinberg]

@pquentin No need to change anything, this is fine. I think this is just that I'm used to handle Python version upgrades differently. My assumption when I saw "Drop 3.7" was that we would just stop testing 3.7, which is what I do for my personal projects (because I intentionally want to let people continue using the dropped version even after I stopped testing it or supporting it). Your meaning of "Drop 3.7" is larger in scope than mine. :)

[pquentin]

Ah right! When I drop a version, I update python_requires, so anyone still using Python 3.7 will be stuck on 8.14. And it's the best moment to drop all the workarounds that were need for previous versions. In the early 3.x days, many changes were related to the ssl module, and now it's mostly typing.

That said your approach could help me for 7.17.