As with all of our other modules, in internal.io_handling we catch all imports from typing because of issues with CPython 3.5.0 and 3.5.1.

In 1.1.6, we removed the dependency on typingbecause I had thought that we only used imports from typing in our Python-2-compatible typehints.

However, in internal.io_handling, we use typing.cast.

This only does anything when the file is being processed by mypy or a similar analyzer, so a quick fix for this is for us to just assign a no-op lambda to cast in the import catch statement.

However, I am concerned that our CI did not catch this...I would like to find out what happened there too.