Extensions add additional features to pyApp.

The extension interface was completely redesigned for pyApp 4.0 to make the let extensions provide far more functionality.

Extensions can:

  • Provide default_settings

  • Register checks

  • Add commands to the CLI

  • Register factories with the injection framework.


Extensions developed for previous versions of pyApp need to be upgraded to work with pyApp 4.

Using extensions

Once an extension has been installed it is immediately available in pyApp. The CLI extensions command will list all installed extensions. When starting an application additional settings files will show up being loaded.

Control of the extension version and availability of extensions is left up to the standard packaging tools and processes. I would recommend using pipenv or poetry to manage your applications dependencies (along with extensions). If you project has specific security requirements a whitelist can be provided to CliApplication to only allow specific extensions.

Developing an extension

An extension is a normal Python package that follows the pyApp extension protocol.

Extensions must provide a setuptools entry point, this is how they are identified by pyApp and loaded.

In a setup.py file:

    entry_points={'pyapp.extensions': 'my-extension = my_extension:Extension'}

or setup.cfg file:

pyapp.extensions =
    my-extension = my_extension:Extension

Any name or names (if the package provides multiple extensions) can be used for the extension. The entry my_extension:Extension refers to a class called Extension in the my_extension package.

The extension class requires no specific base class and duck typing is used to determine what functions the extension provides.

The following attributes/methods are used by pyApp:


A string that specifies a module that provides default settings. This can be a relative import.


A string that specifies a module that registers additional checks. This can be a relative import.

def register_commands(root: CommandGroup)

A method that is called at startup to allow the extension to register additional commands. This happens early in the startup process prior to settings being loaded.

def ready()

The application has been successfully started and is ready. This is an opportunity to register any custom functionality with pyApp.

An example extension class:

class Extension:
    default_settings = ".default_settings"
    checks = ".checks"

    def register_commands(root: CommandGroup):
        # Register a group and commands
        group = root.create_command_group("foo")

        def bar(opts):
            Do a foo bar operation.

    def ready():