def walk(self):
        yield self
        for c in self.children():
            for x in c.walk():
                yield x
Implementation of - operator when left operand is not a ParserElement
dataset/ETHPy150Open uwescience/raco/raco/algebra.py/Operator.walk--crossover with--dataset/ETHPy150Open ipython/ipython-py3k/IPython/external/pyparsing/_pyparsing.py/ParserElement.__rsub__