Extending The App Object

The App.extend() method provides a mechanism that allows plugins, extensions, or the app itself to add objects or functions to the global application object.

For example, a plugin might extend the App with an api member allowing developers to call app.api.get(...). The application itself does not provide app.api. However, the plugin does. As plugins are often third party, it is not possible for the plugin developer to simply sub-class the App class and add the functionality because the class is already instantiated by the time plugins are loaded.

Example: Extending the App Object

from cement import App

def example_func():
    print('Inside example_func')

def extend_myapp(app):
    app.extend('example', example_func)

class MyApp(App):
    class Meta:
        label = 'myapp'
        hooks = [
            ('post_setup', extend_myapp),
        ]

with MyApp() as app:
    app.run()

    # call the extended object or function
    app.example()

Alternatively from within an extension or plugin:

def example_func():
    print('Inside example_func')

def extend_myapp(app):
    app.extend('example', example_func)

def load(app):
    app.hook.register('post_setup', extend_myapp)

cli

Extended members can be anything from instantiated objects to callables of any kind. Its use case is varied and arbitrary... but should be documented well by the developer that is extending it.