Change effective on 17 December 2016
Heroku now supports Python 2.7.13. You can specify a version with a
Python 2.7.13 is now default for all new Python applications. Existing applications will not be automatically updated.
This build of Python was built with UCS-4 mode enabled (as opposed to the previously-used UCS-2 mode). This will improve unicode support, as well as compatibility with many pre-built Linux wheels available in the Python ecosystem.
Build tools were also updated: setuptools to v32.1.0.