Part 7: Other Changes

Creating diagnostics

When the app does not work as expected, the user should know what is happening with the app. FreedomBox framework provides an API for running and showing diagnostics results. Most of the common diagnostic tests are implemented by the framework as part of the components used by an app. FreedomBox takes care of calling the diagnostics method and displaying the list in a formatted manner.

To implement additional diagnostic tests on top of those provided by the framework, the method plinth.app.App.diagnose() has to be overridden or in a component that belongs to the app, the method plinth.app.Component.diagnose() has to be overridden. The methods must return a list in which each item is the result of a test performed. The item itself is a two-tuple containing the display name of the test followed by the result as passed, failed or error.

views.py

class TransmissionAppView(views.AppView):
    ...
    def diagnose():
        """Run diagnostics and return the results."""
        results = super().diagnose()

        results.append(['Example test', 'passed'])

        return results

The user can trigger the diagnostics test by going to System -> Diagnostics page. This runs diagnostics for all the applications. Users can also run diagnostics specifically for this app from the app’s page. A diagnostics menu item is shown by the plinth.views.AppView and app.html template automatically when diagnose() method is overridden in the app or a component.

Logging

Sometimes we may feel the need to write some debug messages to the console and system logs. Doing this in FreedomBox is just like doing this any other Python application.

views.py

import logging

logger = logging.getLogger(__name__)

def example_method():
    logger.debug('A debug level message')

    logger.info('Showing application page - %s', request.method)

    try:
        something()
    except Exception as exception:
        # Print stack trace
        logger.exception('Encountered an exception - %s', exception)

For more information see Python logging framework documentation.

Internationalization

Every string message that is visible to the user must be localized to user’s native language. For this to happen, our app needs to be internationalized. This requires marking the user visible messages for translation. FreedomBox apps use the Django’s localization methods to make that happen.

__init__.py

from django.utils.translation import gettext_lazy as _

class TransmissionApp(app_module.App):
    ...

    def __init__(self):
      ...

      info = app_module.Info(...
                             name=_('Transmission'),
                             ...
                             short_description=_('BitTorrent Web Client'),
                             ...)

Notice that the app’s name, description, etc. are wrapped in the _() method call. This needs to be done for the rest of our app. We use the gettext_lazy in some cases and we use the regular gettext in other cases. This is because in the second case the gettext lookup is made once and reused for every user looking at the interface. These users may each have a different language set for their interface. Lookup made for one language for a user should not be used for other users. The _lazy methods provided by Django makes sure that the return value is an object that will actually be converted to string at the final moment when the string is being displayed. In the first case, the lookup is made and string is returned immediately.

All of this is the usual way internationalization is done in Django. See Internationalization and localization documentation for more information.