mypy: Static Type Checking Command Reference

Catch type errors before runtime.

mypy statically checks Python type annotations, flagging mismatches before they reach runtime. CI runs it as a gate so type regressions fail the build.

Common flags / usage

mypy src/ -- type-check a package or path
--strict -- enable the full set of strict checks
--ignore-missing-imports -- skip unresolved third-party imports
--install-types --non-interactive -- fetch missing stub packages
--cache-dir DIR -- control the incremental cache location

Example

shell

- run: pip install mypy
- uses: actions/cache@v4
  with:
    path: .mypy_cache
    key: mypy-${{ hashFiles('**/*.py') }}
- run: mypy --strict src/

In CI

mypy is incremental -- cache .mypy_cache across runs for a big speedup. Missing third-party stubs cause errors; install stub packages (or run --install-types --non-interactive) rather than blanket --ignore-missing-imports, which hides real issues.

Key takeaways

mypy gates the build on static type-checking errors.
Cache .mypy_cache to make repeated CI runs much faster.
Install type stubs instead of broadly ignoring missing imports.