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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 get_session(self, app_path, session_id):
        ''' Get an active a session by name application path and session ID.

        Args:
            app_path (str) :
                The configured application path for the application to return
                a session for.

            session_id (str) :
                The session ID of the session to retrieve.

        Returns:
            ServerSession

        '''
        if app_path not in self._applications:
            raise ValueError("Application %s does not exist on this server" % app_path)
        return self._applications[app_path].get_session(session_id)