* `#error BYE_BYE_GOLDEN_SNAKE`
* Removing everything related to 2.7 from ci.yml
* Commenting-out Centos7
* Removing `PYTHON: 27` from .appveyor.yml
* "PY2" removal, mainly from tests. C++ code is not touched.
* Systematic removal of `u` prefix from `u"..."` and `u'...'` literals. Collateral cleanup of a couple minor other things.
* Cleaning up around case-insensitive hits for `[^a-z]py.*2` in tests/.
* Removing obsolete Python 2 mention in compiling.rst
* Proper `#error` for Python 2.
* Using PY_VERSION_HEX to guard `#error "PYTHON 2 IS NO LONGER SUPPORTED.`
* chore: bump pre-commit
* style: run pre-commit for pyupgrade 3+
* tests: use sys.version_info, not PY
* chore: more Python 2 removal
* Uncommenting Centos7 block (PR #3691 showed that it is working again).
* Update pre-commit hooks
* Fix pre-commit hook
* refactor: remove Python 2 from CMake
* refactor: remove Python 2 from setup code
* refactor: simplify, better static typing
* feat: fail with nice messages
* refactor: drop Python 2 C++ code
* docs: cleanup for Python 3
* revert: intree
revert: intree
* docs: minor touchup to py2 statement
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>
