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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 describe_schema_versions(self, ):
 """ for each schema version present in the cluster, returns a list of nodes at that version. hosts that do not respond will be under the key DatabaseDescriptor.INITIAL_VERSION. the cluster is all on the same version if the size of the map is 1. """

    self._seqid += 1
    d = self._reqs[self._seqid] = defer.Deferred()
    self.send_describe_schema_versions()
    return d