def ancestorset(self, starts, stops=None):
    '\n        set of all ancestors of starts (incl), but stop walk at stops (excl)\n        '
    raise NotImplementedError()
set of all ancestors of starts (incl), but stop walk at stops (excl)
def ancestorset(self, starts, stops=None):
    '\n        \n        '
    raise NotImplementedError()