Pyupgrade to 3.9

[daveisfera]

Minimum version of 3.9
Add up to 3.13
Build improvements

[ikoruk]

Hi @jparise is there any chance of getting this PR reviewed and pushed upstream? It would be nice to use a pymemcache that officially supports the newer Pythons.

[jparise]

Hi @jparise is there any chance of getting this PR reviewed and pushed upstream? It would be nice to use a pymemcache that officially supports the newer Pythons.

I no longer work at Pinterest or use pymemcache on a regular basis, but I'll try to block out some time soon to help work through the backlog of open pull requests.

[daveisfera]

I no longer work at Pinterest or use pymemcache on a regular basis, but I'll try to block out some time soon to help work through the backlog of open pull requests.

Thanks! This should be a really low risk change so hopefully should be an easy one to click merge on

[jparise]

I no longer work at Pinterest or use pymemcache on a regular basis, but I'll try to block out some time soon to help work through the backlog of open pull requests.

Thanks! This should be a really low risk change so hopefully should be an easy one to click merge on

I'm afraid I no longer have that level of access (and I'm also not a CODEREVIEWER).

A @pinterest/pymemcache person will need to step in.

[cclauss]

Nice!

[yurushao]

The Lint step also failed on master branch. Probably not related to this PR.

[cclauss]

black --check .
would reformat pymemcache/client/base.py

[daveisfera]

black --check .
would reformat pymemcache/client/base.py

Pushed a commit to apply the change that black wanted