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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:
 async def set(self, key, value, param=None, expire_time=None, herd_timeout=None):
 """ Use key and param to generate identity and pack the content, expire the key within real_timeout if expire_time is given. real_timeout is equal to the sum of expire_time and herd_time. The content is cached with expire_time. """

        identity = self._gen_identity(key, param)
        expected_expired_ts = int(time.time())
        if expire_time:
            expected_expired_ts += expire_time
        expected_expired_ts += herd_timeout or self.default_herd_timeout
        value = self._pack([value, expected_expired_ts])
        return await self.client.set(identity, value, ex=expire_time)