Checklist for dropping Python 2 in my libraries

dropping_py2.md

• Add pyupgrade to .pre-commit-config.yaml.

If supporting py35, use --py3-plus instead of --py37-plus.

- repo: https://github.com/asottile/pyupgrade
  rev: ...latest version...
  hooks:
  - id: pyupgrade
    args: [--py37-plus]

• Run pre-commit (usually tox -e lint in my projects).
• Remove unnecessary __future__ imports.
• Update setup.py: remove classifiers and add/update python_requires

    python_requires=">=3.7",

• Remove conditional installs e.g. 'flake8-bugbear==19.8.0; python_version >= "3.5"' from setup.py and pre-commit-config.yaml.
• Update tox.ini and CI config (azure-pipelines.yml or .travis.yml).
• Update installation/requirements and contributing docs.
• Update pyproject.yml (black) if it exists.
• Remove compatibility code: compat.py, sys.version_info checks, try:..except ImportError:
• Use keyword-only arguments where sensible.
• Update changelog.

Thanks @hugovk. I don't use six in my projects, but good reminder about sys.version_info and try-excepts. Updated the list with a note about those.