common python form of networkx's implementation of Johnson's cycle finding algorithm

johnson.py

from collections import defaultdict
def simple_cycles(G):

    def _unblock(thisnode,blocked,B):
        stack = set([thisnode])
        while stack:
            node = stack.pop()
            if node in blocked:
                blocked.remove(node)
                stack.update(B[node])
                B[node].clear()

    startnode = G.keys()[0]
    path=[startnode]
    blocked = set()
    closed = set()
    blocked.add(startnode)
    B=defaultdict(set)
    stack=[ (startnode,list(G[startnode])) ]
    while stack:
        thisnode, nbrs = stack[-1]
        if nbrs:
            nextnode = nbrs.pop()
            if nextnode == startnode:
                yield path[:]
                closed.update(path)
            elif nextnode not in blocked:
                path.append(nextnode)
                stack.append( (nextnode,list(G[nextnode])) )
                closed.discard(nextnode)
                blocked.add(nextnode)
                continue
        if not nbrs:
            if thisnode in closed:
                _unblock(thisnode,blocked,B)
            else:
                for nbr in G[thisnode]:
                    if thisnode not in B[nbr]:
                        B[nbr].add(thisnode)
            stack.pop()
            path.pop()

graph = {0: [7, 3, 5], 1: [2], 2: [7, 1], 3: [0, 5], 4: [6, 8], 5: [0, 3, 7], 6: [4, 8], 7: [0, 2, 5, 8], 8: [4, 6, 7]}
print(tuple(simple_cycles(graph)))

Not working