def root_nodes(self):
        return self.filter(**{'%s__isnull' % self.parent_attr: True})
Implementation of ^ operator - returns Or
dataset/ETHPy150Open agiliq/django-socialnews/socialnews/mptt/managers.py/TreeManager.root_nodes--crossover with--dataset/ETHPy150Open ipython/ipython-py3k/IPython/external/pyparsing/_pyparsing.py/ParserElement.__xor__