mypy is only a static checker, there are no runtime-checks inserted. You run it as a command-line tool and it will fail the build if the types do not resolve, l

mypy is only a static checker, there are no runtime-checks inserted. You run it as a command-line tool and it will fail the build if the types do not resolve, like a compiler or linting tool. For runtime-checking based on PEP484 type hints, one can complement this with a library like Pydantic/Enforce.py/typeguard/typesentry. Enforcement of the types is typically opt-in per function call, often by adding a decorator.