def __setstate__(self, state):
        super(VariableTree, self).__setstate__(state)
        if self._parent_ref is not None:
            self._parent_ref = weakref.ref(self._parent_ref)
Cut a matrix expression into Blocks
dataset/ETHPy150Open OpenMDAO/OpenMDAO-Framework/openmdao.main/src/openmdao/main/vartree.py/VariableTree.__setstate__--crossover with--dataset/ETHPy150Open sympy/sympy/sympy/matrices/expressions/blockmatrix.py/blockcut