def __init__(self):
        if (self.compare is None) != (self.version is None):
            raise ValueError(
                "Must specify both or neither compare and version.")
Update and return an object.
dataset/ETHPy150Open ClusterHQ/flocker/admin/packaging.py/Dependency.__init__--crossover with--dataset/ETHPy150Open namlook/mongokit/mongokit/document.py/Document.find_and_modify