def add_parent(self, parent):
        """Add a parent node."""
        assert isinstance(parent, TreeNode)
        if self.parents not in parent:
            self.parents.append(parent)
dataset/ETHPy150Open VisTrails/VisTrails/vistrails/packages/vtk/vtk_wrapper/class_tree.py/TreeNode.add_parent/swapped operands of `not in`