Python：使用递归时出错

Question

我已经写了一个函数，我试着调用它一些但是它给我一个错误。

# create a graph with all active nodes

G = nx.erdos_renyi_graph(100, 0.05)
pos = nx.spring_layout(G)
G.add_nodes_from(G.nodes(), color='blue')
nx.draw_networkx_nodes(G, pos, G.nodes(), node_size=20, node_color='b')
nx.draw_networkx_edges(G, pos, alpha=0.3)

def step(G, x, y):
color = nx.get_node_attributes(G, 'color')
for (key, value) in zip(color, color.values()):
    if value == 'blue':
        neighbours = G.neighbors(key)
        inactive_neighbours = []
        for n in neighbours:
            if color[n] == 'red':
                inactive_neighbours.append(n)
                if inactive_neighbours:
                    chosen_neighbour = random.sample(neighbours, 1)
                    if np.random.random() < x / (x + y):
                        activate = []
                        activate.append(chosen_neighbour)
                        G.add_nodes_from(activate, color='blue')

        if np.random.random() < y / (x + y):
            deactivate = []
            deactivate.append(key)
            G.add_nodes_from(deactivate, color='red')

print(nx.get_node_attributes(G, 'color'))
i = 3
while 2 < i < 100:
    step(G, 0.5, 1)
    i += 1

step(G, 0.5, 1)

它会让我失误 ValueError: not enough values to unpack (expected 2, got 1)。 我做错了什么？ 我怎样才能调用函数来执行它？