Specifying a Python Runtime

Last updated 01 March 2018

Heroku’s Python support extends to the latest stable release from the Python 3.6.x and Python 2.7.x series.

Today, this support extends to these specific runtimes:

• python-3.6.4
• python-2.7.14

Selecting a runtime

Newly created Python applications default to the Python 3.6.4 runtime.

You can specify an explicit version of Python to be used to run your application. For example, if you require Python 2, add the following to your Pipfile:

[requires]
python_version = "2.7"

Or, more specifically:

[requires]
python_full_version = "2.7.14"

Then, run $ pipenv lock to generate the appropriate Pipfile.lock, and push it to Heroku.

Alternatively, (e.g. if you’re using pip), you can also supply a runtime.txt file:

$ cat runtime.txt
python-2.7.14

Note: When changing Python runtime versions, all dependencies need to be re–installed.