In python 2.7 they also introduced "bytes" although it was just another alias to "str". I wonder if they would make python 2.7 distinguish between them and add an option (like another import from __future__) to throw errors when these types were mixed.

This would help a lot in preparing code incrementally to work on python3.

In the mean time, mypy in python 2 mode doesn't warn about str <-> bytes either :/