Python runtime defaults to 3.6.1

Change effective on 20 June 2017

Effective today, new Python applications pushed to Heroku will use the python-3.6.1 runtime by default (instead of python-2.7.13).

Existing applications are not affected by this change.

If you would like to specify Python 2.7, rather than using the new default, please refer to the Heroku Dev Center.