Heroku Python Support

Last Updated: 27 May 2015

cedar django python

Table of Contents

This document describes the general behavior of the Heroku Cedar stack as it relates to the recognition and execution of Python applications. Pure Python applications, such as headless processes and evented web frameworks like Twisted, are fully supported. All versions of Django are fully supported. Django applications are detected by the presence of a manage.py file within the repository.

For framework-specific tutorials please see:

Activation

The Heroku Python Support will be applied to applications only when the application has a requirements.txt in the root directory. Even if an application has no module dependencies, it should include an empty requirements.txt to document that your app has no dependencies.

When a deployed application is recognized as a Python application, Heroku responds with -----> Python app detected.

$ git push heroku master
-----> Python app detected

Process types

No default web process types are created if a Python application is detected. See the Getting Started with Python on Heroku tutorial for information about how to set up your Procfile.

Supported Python Runtimes

Newly created Python applications default to the Python 2.7.10 runtime.

You can specify an arbitrary version of Python to be used to run your application. This functionality is enabled by the presence of a runtime.txt file.

$ cat runtime.txt
python-2.7.10

Supported Runtimes

  • python-2.7.10
  • python-3.4.3

Unsupported Runtimes

Unsupported runtimes can also be specified (2.4.4–3.4.3). However, we only endorse and support the use of Python 2.7.10 and 3.4.3.

Changing runtimes

If you specify a different Python runtime than a previous build, your application’s build cache will be purged.

Libraries

The following libraries are used by the platform for managing and running Python applications and cannot be specified.

  • Setuptools 16.0: Python packaging tools.
  • Pip 7.0.1: Application dependency resolution.

Build behavior

The following command is run on your app to resolve dependencies:

$ pip install -r requirements.txt --allow-all-external

The .heroku directory is cached between pushes to speed up package installation.

Add-ons

For Django applications, a Heroku Postgres hobby-dev database is automatically provisioned. This populates the DATABASE_URL environment variable.

No add-ons are automatically provisioned if a pure Python application is detected. If you need a SQL database for your app, add one explicitly:

$ heroku addons:create heroku-postgresql:hobby-dev