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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 unwatch_source(self, source_id):
 """ Remove a souce from the watchlist. """

        source_id = int(source_id)
        self._watched_sources.remove(source_id)
        return (yield from
                self._send_cmd("WATCH S[%d] OFF" % (
                    source_id, )))