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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 broadcast(self, channel, event, data):
 """Broadcasts an event to all sockets listening on a channel."""

        payload = self._server.serialize_event(event, data)
        for socket_id in self.subscriptions.get(channel, ()):
            rv = self._server.sockets.get(socket_id)
            if rv is not None:
                rv.socket.send(payload)