For the most part, dropping support of old Python versions is the opposite of support new Python version, but with a few more checks.

As per our policy, we aim to support Python versions for at least 42 months (or 36 months if it's troublesome for some reason). In practice, we can probably support versions of Python for longer, b/c it does not cost us any extra CI time (b/c we choose versions randomly). If supporting an extra-old version of Python ever becomes a nuisance, or if we want new features available in the next Python version, then by all means drop support for it! It may also be interesting to look at download data to see usage of different versions.

• Remove "py3x" from [tool.black.target-version]
• Remove "Programming Language :: Python :: 3.x", from [project.classifiers]
• Remove unnecessary warning filters in [tool.pytest.ini_options.filterwarnings]
• Update [tool.ruff.target-version] to next version, such as "py39"
• Update minimum dependency versions in pyproject.toml (dependencies and optional-dependencies) to match what we test
  • (Optional) Also, removing support of a Python version is a natural time to remove supported versions of dependencies, which we may support for much longer than 24 months if it's trivial to do so.

• Remove 3.x option from random pyver (and its weight)

• Remove 3.x option from random pyver (and its weight)
• Delete if branch under "Update env" task for this Python version
  • Note that this can, in effect, increase the minimum supported version of a dependency

• Update args of pyupgrade pre-commit, such as args: [--py39-plus]

Update versions under python-version: in e.g. CI scripts. Find them:

• $ git grep 'python-version.*3.8'

As a sanity check, perform a search to see if there are any lingering items (you can also start with this step!)

• $ git grep 3\.8
• $ git grep py38
• $ git grep MAINT

Update Python version in binder/environment.yml and docs/env.yml whenever.

Finally, be aware of any other new Python features that are now available to use and whether any from __future__ import whatever are no longer needed. Sometimes, the linters as part of pre-commit will update or flag things for us.