Harmonise return type of builtins.__import__ and importlib.import_module

[AlexWaygood]

This PR is an attempt at solving #6295 by adding __getattr__ to types.ModuleType and changing the return type of builtins.__import__ so that it now returns types.ModuleType rather than Any.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

isort (https://github.com/pycqa/isort.git)
+ isort/_future/__init__.py:9: error: unused "type: ignore" comment
+ isort/_future/__init__.py:10: error: unused "type: ignore" comment
+ isort/output.py:504: error: unused "type: ignore" comment
+ isort/output.py:516: error: unused "type: ignore" comment
+ isort/output.py:523: error: unused "type: ignore" comment

pip (https://github.com/pypa/pip.git)
- src/pip/_internal/locations/__init__.py:68: error: Module has no attribute "platlibdir"
+ src/pip/_internal/network/session.py:106: error: unused "type: ignore" comment

kornia (https://github.com/kornia/kornia.git)
- kornia/testing/__init__.py:16: error: Module has no attribute "util"  [attr-defined]

ibis (https://github.com/ibis-project/ibis.git)
- ibis/backends/tests/conftest.py:45: error: Module has no attribute "TestConf"

python-chess (https://github.com/niklasf/python-chess.git)
+ chess/engine.py:122: error: unused "type: ignore" comment
+ chess/engine.py:123: error: unused "type: ignore" comment
+ chess/engine.py:1209: error: unused "type: ignore" comment

anyio (https://github.com/agronholm/anyio.git)
+ src/anyio/_core/_eventloop.py:56: error: unused "type: ignore" comment

sphinx (https://github.com/sphinx-doc/sphinx.git)
+ sphinx/util/typing.py:228: error: unused "type: ignore" comment
+ sphinx/util/typing.py:428: error: unused "type: ignore" comment
+ sphinx/util/inspect.py:424: error: unused "type: ignore" comment
+ sphinx/util/inspect.py:427: error: unused "type: ignore" comment
+ sphinx/util/inspect.py:430: error: unused "type: ignore" comment
+ sphinx/util/docutils.py:52: error: unused "type: ignore" comment
+ sphinx/util/docutils.py:53: error: unused "type: ignore" comment
+ sphinx/util/docutils.py:67: error: unused "type: ignore" comment
+ sphinx/util/docutils.py:81: error: unused "type: ignore" comment
+ sphinx/util/docutils.py:95: error: unused "type: ignore" comment
+ sphinx/util/docutils.py:110: error: unused "type: ignore" comment
+ sphinx/domains/python.py:1452: error: unused "type: ignore" comment
+ sphinx/writers/manpage.py:110: error: unused "type: ignore" comment
+ sphinx/testing/util.py:126: error: unused "type: ignore" comment
+ sphinx/testing/util.py:127: error: unused "type: ignore" comment
+ sphinx/util/compat.py:29: error: unused "type: ignore" comment

aiohttp (https://github.com/aio-libs/aiohttp.git)
+ aiohttp/connector.py:1306: error: unused "type: ignore" comment
+ aiohttp/web_runner.py:181: error: unused "type: ignore" comment
+ aiohttp/pytest_plugin.py:244: error: unused "type: ignore" comment

streamlit (https://github.com/streamlit/streamlit.git)
+ lib/streamlit/script_runner.py:432: error: unused "type: ignore" comment
+ lib/streamlit/script_runner.py:439: error: unused "type: ignore" comment

werkzeug (https://github.com/pallets/werkzeug.git)
+ src/werkzeug/_reloader.py:20: error: unused "type: ignore" comment
- tests/test_wrappers.py:833: note: Use "-> None" if function does not return a value
- tests/test_wrappers.py:856: note: (Skipping most remaining errors due to unresolved imports or missing stubs; fix these first)
+ tests/test_wrappers.py:833: note: (Skipping most remaining errors due to unresolved imports or missing stubs; fix these first)

core (https://github.com/home-assistant/core.git)
+ homeassistant/components/http/forwarded.py:91: error: unused "type: ignore" comment
+ homeassistant/auth/mfa_modules/__init__.py:136: error: unused "type: ignore" comment
+ homeassistant/auth/mfa_modules/__init__.py:171: error: unused "type: ignore" comment
+ homeassistant/auth/providers/__init__.py:145: error: unused "type: ignore" comment
+ homeassistant/auth/providers/__init__.py:178: error: unused "type: ignore" comment
+ homeassistant/config.py:648: error: unused "type: ignore" comment
+ homeassistant/config.py:651: error: unused "type: ignore" comment
+ homeassistant/config.py:662: error: unused "type: ignore" comment
+ homeassistant/config.py:672: error: unused "type: ignore" comment
+ homeassistant/config.py:673: error: unused "type: ignore" comment
+ homeassistant/config.py:753: error: unused "type: ignore" comment
+ homeassistant/config.py:895: error: unused "type: ignore" comment
+ homeassistant/setup.py:241: error: unused "type: ignore" comment
+ homeassistant/setup.py:246: error: unused "type: ignore" comment
+ homeassistant/helpers/check_config.py:161: error: unused "type: ignore" comment
+ homeassistant/config_entries.py:304: error: unused "type: ignore" comment
+ homeassistant/config_entries.py:443: error: unused "type: ignore" comment
+ homeassistant/config_entries.py:482: error: unused "type: ignore" comment
+ homeassistant/config_entries.py:519: error: unused "type: ignore" comment
+ homeassistant/helpers/condition.py:929: error: unused "type: ignore" comment
+ homeassistant/helpers/condition.py:977: error: unused "type: ignore" comment
+ homeassistant/helpers/script.py:260: error: unused "type: ignore" comment
+ homeassistant/helpers/script.py:262: error: unused "type: ignore" comment
+ homeassistant/helpers/script.py:269: error: unused "type: ignore" comment
+ homeassistant/scripts/__init__.py:67: error: unused "type: ignore" comment
+ homeassistant/helpers/reload.py:81: error: unused "type: ignore" comment
+ homeassistant/helpers/reload.py:82: error: unused "type: ignore" comment
+ homeassistant/components/notify/legacy.py:61: error: unused "type: ignore" comment
+ homeassistant/components/notify/legacy.py:66: error: unused "type: ignore" comment
+ homeassistant/components/device_tracker/legacy.py:241: error: unused "type: ignore" comment
+ homeassistant/components/device_tracker/legacy.py:246: error: unused "type: ignore" comment
+ homeassistant/components/device_tracker/legacy.py:251: error: unused "type: ignore" comment
+ homeassistant/components/device_tracker/legacy.py:256: error: unused "type: ignore" comment

edgedb (https://github.com/edgedb/edgedb.git)
+ edb/server/pgconnparams.py:75: error: unused "type: ignore" comment

[AlexWaygood]

Diff from mypy_primer, showing the effect of this PR on open source code:

[...]

This seems like it just makes a lot of people's lives easier, if they were just switching off the type-checker whenever they were doing a dynamic import.

[srittau]

Looks quite promising. Waiting for @JelleZijlstra's input.

[AlexWaygood]

Thanks, both! 😀