<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def init_app(self, app):
 """ This callback can be used to initialize an application for the use with this prometheus reporter setup. This is usually used with a flask "app factory" configuration. Please see: http://flask.pocoo.org/docs/1.0/patterns/appfactories/ for this mode, otherwise it is called automatically. :param app: the Flask application """


        if self.path:
            self.register_endpoint(self.path, app)

        if self._export_defaults:
            self.export_defaults(
                self.buckets, self.group_by,
                self._defaults_prefix, app
            )