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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 _start(self, request_id, docs):
 """Publish a CommandStartedEvent."""

        cmd = self.command.copy()
        cmd[self.field] = docs
        self.listeners.publish_command_start(
            cmd, self.db_name,
            request_id, self.sock_info.address, self.op_id)
        return cmd