Time to drop Python 3.6?

[cclauss]

Next week Python 3.11 will be released and we are already testing release candidate 2 on GitHub Actions.

Supporting six different versions of CPython is a big ask. Is it time to drop support for Python 3.6?

• https://devguide.python.org/versions

[xlcnd]

I am working on a new version of isbnlib (series 4.X.X) that will break compatibility and is an opportunity to modernize the code base and reconsider the versions of python supported.

However, I would like to keep the series 3.X.X as compatible as possible with older versions.