Scheduling tasks with Cron

We have designed the shrink operation as an optional functionality triggered by users, but we could run it at a determined time interval for every user in order to lower the costs of Cloud Storage. App Engine supports the scheduled execution of jobs with the Cron service; every application has a limited number of Cron jobs available, depending on our billing plan. Cron jobs have the same restrictions as tasks in a task queue, so the request can last up to 10 minutes.

We first prepare a request handler that will implement the job:

class ShrinkCronJob(ShrinkHandler):
    def post(self):
        self.abort(405, headers=[('Allow', 'GET')])

    def get(self):
        if 'X-AppEngine-Cron' not in self.request.headers:
            self.error(403)

        notes = Note.query().fetch()
        for note in notes:
            self._shrink_note(note)

We derive the ShrinkCronJob class from the ShrinkHandler class to inherit the _shrink_note() method...