To backport `os.path.commonpath` in mypy I needed to use genericpath. It seems unchanged since 3.4, and the `same*` functions were added in 3.4. (checked via comparing the `__all__`s of the source in 2.7, 3.4, and 3.7.)
This module is going to be used by mypy for the daemon on Windows. To that end I ran stubgen on _winapi, then read through Modules/_winapi.c to add the function types. This seems to have been added in Python 3.1, but I think it is completely fine to just leave it in stdlib/3.
Mypy has issues with running its test suite with many processes
concurrently. This should reduce travis test failures, if not completely
resolve failures. See issue https://github.com/python/mypy/issues/3543