regex.py 文件源码

def up(self, visited: FrozenSet[Any]=None) -> Set[Any]:
        """ Returns the set of reachable nodes by going up on this node """
        if visited is None:
            visited = frozenset()

        if self.symbol == '|':
            # skip the whole right sub tree
            node = self.right
            while node.symbol == '.' or node.symbol == '|':
                node = node.right
            return node.right.up(visited)
        elif self.symbol == '.':
            return self.right.down(visited)
        elif self.symbol == '*':
            return self.left.down(visited) | self.right.up(visited)
        elif self.symbol == '?':
            return self.right.up(visited)
        else:  # self.symbol == END:
            return {self}