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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 sequential_id(self, client):
 """Return the sequential id for this test for the passed in client"""

        if client.client_id not in self._sequential_ids:
            id_ = sequential_id("e:{0}:users".format(self.name), client.client_id)
            self._sequential_ids[client.client_id] = id_
        return self._sequential_ids[client.client_id]