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# `pycassa` - Exceptions and Enums

exception `pycassa.``AuthenticationException`

  The credentials supplied when creating a connection did not validate, indicating a bad username or password.

exception `pycassa.``AuthorizationException`

  The user that is currently logged in for a connection was not permitted to perform an action.

exception `pycassa.``InvalidRequestException`

  Something about the request made was invalid or malformed. The request should not be repeated without modification. Sometimes checking the server logs may help debug what was wrong with the request.

exception `pycassa.``NotFoundException`

  The row requested does not exist, or the slice requested was empty.

exception `pycassa.``UnavailableException`

  Not enough replicas are up to satisfy the requested consistency level.

exception `pycassa.``TimedOutException`

  The replica node did not respond to the coordinator node within `rpc_timeout_in_ms` (as configured in `cassandra.yaml`), typically indicating that the replica is overloaded or just went down.

class `pycassa.``ConsistencyLevel`
  `ANY`

    Only requires that one replica receives the write or the coordinator stores a hint to replay later. Valid only for writes.

  `ONE`

    Only one replica needs to respond to consider the operation a success

  `QUORUM`

    ceil(RF/2) replicas must respond to consider the operation a success

  `ALL`

    All replicas must respond to consider the operation a success

  `LOCAL_QUORUM`

    Requres a quorum of replicas in the local datacenter

  `LOCAL_ONE`

    Has the same behavior as ONE, except that Only replicas in the local datacenter are sent queries

  `EACH_QUORUM`

    Requres a quorum of replicas in each datacenter

  `TWO`

    Two replicas must respond to consider the operation a success

  `THREE`

    Three replicas must respond to consider the operation a success

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