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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def init_app(self, app, client_id=None):
 """Initialize the Micropub extension if it was not given app in the constructor. Args: app (flask.Flask):
 the flask application to extend. client_id (string, optional):
 the IndieAuth client id, will be displayed when the user is asked to authorize this client. If not provided, the app name will be used. """

        if not self.client_id:
            if client_id:
                self.client_id = client_id
            else:
                self.client_id = app.name