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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 id(cls):
 """ Database identity for this model, used for foreign key references from other models """

        if cls.__uuid_primary_key__:
            return immutable(Column(UUIDType(binary=False), default=uuid_.uuid4, primary_key=True, nullable=False))
        else:
            return immutable(Column(Integer, primary_key=True, nullable=False))