Python 2 removal part 1: tests (C++ code is intentionally ~untouched) (#3688)

* `#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>

.pre-commit-config.yaml

@@ -29,14 +29,15 @@ repos:
   - id: mixed-line-ending
   - id: requirements-txt-fixer
   - id: trailing-whitespace
-  - id: fix-encoding-pragma
-    exclude: ^noxfile.py$
 
+# Upgrade old Python syntax
 - repo: https://github.com/asottile/pyupgrade
   rev: v2.31.0
   hooks:
   - id: pyupgrade
+    args: [--py3-plus]
 
+# Nicely sort includes
 - repo: https://github.com/PyCQA/isort
   rev: 5.10.1
   hooks:
@@ -44,20 +45,21 @@ repos:
 
 # Black, the code formatter, natively supports pre-commit
 - repo: https://github.com/psf/black
-  rev: 21.12b0 # Keep in sync with blacken-docs
+  rev: 22.1.0 # Keep in sync with blacken-docs
   hooks:
   - id: black
 
+# Also code format the docs
 - repo: https://github.com/asottile/blacken-docs
-  rev: v1.12.0
+  rev: v1.12.1
   hooks:
   - id: blacken-docs
     additional_dependencies:
-    - black==21.12b0 # keep in sync with black hook
+    - black==22.1.0 # keep in sync with black hook
 
 # Changes tabs to spaces
 - repo: https://github.com/Lucas-C/pre-commit-hooks
-  rev: v1.1.10
+  rev: v1.1.11
   hooks:
   - id: remove-tabs
 
@@ -67,12 +69,15 @@ repos:
   hooks:
   - id: pycln
 
+# Checking for common mistakes
 - repo: https://github.com/pre-commit/pygrep-hooks
   rev: v1.9.0
   hooks:
   - id: python-check-blanket-noqa
   - id: python-check-blanket-type-ignore
   - id: python-no-log-warn
+  # Python 3.6
+  # - id: python-use-type-annotations
   - id: rst-backticks
   - id: rst-directive-colons
   - id: rst-inline-touching-normal
@@ -87,6 +92,7 @@ repos:
       - pep8-naming
     exclude: ^(docs/.*|tools/.*)$
 
+# Automatically remove noqa that are not used
 - repo: https://github.com/asottile/yesqa
   rev: v1.3.0
   hooks:
@@ -107,9 +113,9 @@ repos:
   rev: v0.931
   hooks:
   - id: mypy
-    # Running per-file misbehaves a bit, so just run on all files, it's fast
-    pass_filenames: false
-    additional_dependencies: [typed_ast]
+    args: [--show-error-codes]
+    exclude: ^(tests|docs)/
+    additional_dependencies: [nox, rich]
 
 # Checks the manifest for missing files (native support)
 - repo: https://github.com/mgedmin/check-manifest
@@ -120,6 +126,7 @@ repos:
     stages: [manual]
     additional_dependencies: [cmake, ninja]
 
+# Check for spelling
 - repo: https://github.com/codespell-project/codespell
   rev: v2.1.0
   hooks:
@@ -127,20 +134,22 @@ repos:
     exclude: ".supp$"
     args: ["-L", "nd,ot,thist"]
 
+# Check for common shell mistakes
 - repo: https://github.com/shellcheck-py/shellcheck-py
-  rev: v0.8.0.3
+  rev: v0.8.0.4
   hooks:
   - id: shellcheck
 
-# The original pybind11 checks for a few C++ style items
+# Disallow some common capitalization mistakes
 - repo: local
   hooks:
   - id: disallow-caps
     name: Disallow improper capitalization
     language: pygrep
     entry: PyBind|Numpy|Cmake|CCache|PyTest
-    exclude: .pre-commit-config.yaml
+    exclude: ^\.pre-commit-config.yaml$
 
+# Clang format the codebase automatically
 - repo: https://github.com/pre-commit/mirrors-clang-format
   rev: "v13.0.0"
   hooks: