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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 get(self, field, cluster):
 """Retrieve the value of one cluster."""

        if _is_list(cluster):
            return [self.get(field, c) for c in cluster]
        assert field in self._fields
        default = self._fields[field]
        return self._data.get(cluster, {}).get(field, default)