If you would like to publish a library package to a package repository (e.g. PyPI) for either internal or external use in type checking, packages that supply type information via type comments or annotations in the code should put a py.typed in their package directory.
Support in Mypy : https://mypy.readthedocs.io/en/latest/installed_packages.html The PEP: https://www.python.org/dev/peps/pep-0561/