Use strict typing

This is a Platinum rule. In quality_scale.yaml, it is called strict-typing.

The integration must be fully typed, and listed in the .strict-typing file of core, so mypy checks it with strict settings. Its library must be typed as well, and ship a py.typed file as described in PEP 561.

Python does not check types at runtime, so a wrong type shows up as a bug in front of a user. Type hints let mypy find those bugs before the code is merged. Strict mode makes mypy fail on missing hints, so nothing slips through untyped.

The library matters too. Without a py.typed file, mypy treats everything from the library as Any, and all the hints in the integration that touch the library check nothing.

Add the integration to .strict-typing in the root of the core repository, in alphabetical order:

homeassistant.components.my_integration.*

Then let hassfest update mypy.ini, and run mypy on the integration:

python3 -m script.hassfest -p mypy_config
mypy homeassistant/components/my_integration

With strict typing, use a typed config entry everywhere you get one: in async_setup_entry, async_unload_entry, the platforms, diagnostics, and the options flow. See runtime-data for how to define it:

type MyConfigEntry = ConfigEntry[MyClient]


async def async_setup_entry(
    hass: HomeAssistant, entry: MyConfigEntry
) -> bool:
    """Set up My integration from a config entry."""

See Typing for how core uses type hints and mypy.

• Hassfest, when the rule is done: the integration must be in .strict-typing, and every requirement in its manifest must ship a py.typed file, or have a separate types- stubs package. Hassfest can only check the requirements that are installed in your environment, in the version the manifest asks for.
• Hassfest, when the rule is done together with runtime-data: async_setup_entry, async_unload_entry, and the other entry points in __init__.py, the platforms, diagnostics.py, and the options flow must use a typed config entry, named like MyConfigEntry.
• Pylint warns when a coordinator does not use the typed config entry of the integration (home-assistant-coordinator-untyped-config-entry).
• Mypy runs in CI and in the Git hooks, and fails on type errors.

There are no exceptions to this rule.

• runtime-data: store runtime data in runtime_data.