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Substrate is a base application and set of libraries for making Google App Engine python development easier. It includes a base app with management script, testing already set up, a set of common helper functions (agar), and a serialization library (restler). It also comes with common libraries like webapp2 and pytz ready to go.

Substrate is based on best practices for Google App Engine python learned in developing several real-world applications with many users.

We are tired of seeing App Engine frameworks languish unsupported. For that reason, Substrate is NOT a framework. It is a base application with a set of libraries and helpers. No more, no less.


To install substrate, run:

$ easy_install substrate

To update your substrate installation to the newest release:

$ easy_install --upgrade substrate

To install or update manually, download the PyPI package, (or to stay on the bleeding edge, clone the substrate repository) and run:

$ python install

Creating a new application

To create a new application, run:

$ substrate new your-app-id

This will create a new directory your-app-id and unpack the substrate application libraries in it. The application name in app.yaml will be set to your-app-id.

Or, if you find installing a script to do this for you tedious, you can clone the substrate repository and copy the app directory to create your application.

Upgrading an existing application

If you have an existing application, you can upgrade it to the latest substrate code by updating the substrate package (see Installation) and then running:

$ substrate update ~/development/your-app-id

where ~/development/your-app-id is the application directory (the one containing your app.yaml file) to upgrade. (For example, you could run this in the current directory with .)

This command will NOT touch any of your application's files. Only "substrate files" in the local/substrate and lib/substrate directories plus and in the application directory will be overwritten. You can add new files to local/usr and lib/usr, but do not edit existing "substrate files" or your changes will be lost when upgrading.

Management Console is a management console for your app. It can invoke several commands.

$ ./ shell

Runs a shell against your local application (uses iPython if available).

$ ./ rshell

Runs a remote shell against your application on Google App Engine. To specify a different application ID than what is in your app.yaml, use -A. If your remote API endpoint is not at the default location, you can pass the path as an argument.

$ ./ test

Runs your application's tests. Any additional parameters are passed to the unitetest2 discover command:

$ ./ test --help

Usage: unit2 discover [options]

  -h, --help            show this help message and exit
  -v, --verbose         Verbose output
  -f, --failfast        Stop on first fail or error
  -c, --catch           Catch ctrl-C and display results so far
  -b, --buffer          Buffer stdout and stderr during tests
  -s START, --start-directory=START
                        Directory to start discovery ('.' default)
  -p PATTERN, --pattern=PATTERN
                        Pattern to match tests ('test*.py' default)
  -t TOP, --top-level-directory=TOP
                        Top level directory of project (defaults to start

Adding Your Own Commands will add .py files in the local/usr/manage/substrate_manage_usr/commands directory as commands.

Adding New Libraries to Your App

Substrate stores its libraries in lib/substrate and local/substrate/lib (for libraries that should not be deployed to Google App Engine). Do not add new libraries to these directories as they are removed and re-copied on upgrade.

User libraries can be placed in lib/usr and local/usr/lib. These paths are added to sys.path by env_setup.setup


As noted above, has a test command. This runs all the tests in the tests directory of your application using unittest2. Included with the Substrate base app is a simple "hello world" test that you can run to verify your installation. It is located in tests/handlers/

Substrate includes test helpers located in the agar.test package. agar.test uses google.appengine.ext.testbed to set up your Google App Engine environment fresh before each test run. It is mostly API compatable with the old gaetestbed project, plus new additions.


Substrate is mostly a packaging of other libraries, which have their own licenses. Original code in Substrate is under the MIT license.