Python字典变异

Question

我已经检查了关于这个主题的不同stackoverflow问题，但我仍然不知道为什么即使我使用.copy（）时graph_dict也会发生变异。我对python很新。请帮忙。提前谢谢。

from random import choice
graph_dict = { 
  1: [3,4,2],
  2: [1,4,3],
  3: [1,2,4],
  4: [5,3,2,1],
  5: [4,8,6,7],
  6: [8,7,5],
  7: [5,8,6],
  8: [5,7,6]
}

def contraction(graph_dict_list):
  if len(graph_dict_list) == 2:
    return len(graph_dict_list[list(graph_dict_list.keys())[0]])

  # randomly pick two Vs
  firstV = choice(list(graph_dict_list.keys()))
  secondV = choice(graph_dict_list[firstV])
  # connect other V to the merged 2nd V
  for each in graph_dict_list[firstV]:
    if (each == secondV):
      graph_dict_list[each] = [x for x in graph_dict_list[each] if x != firstV ]
    else:
      graph_dict_list[each] = [secondV if x == firstV else x for x in graph_dict_list[each]]
  # remove 2nd V in picked list(remove the edge)
  graph_dict_list[firstV].remove(secondV)
  # concat picked list to 2nd V list (merge all the edges)
  graph_dict_list[secondV] = graph_dict_list[secondV] + graph_dict_list[firstV]
  # remove the picked list(1st V)
  del graph_dict_list[firstV]
  # remove self loop
  graph_dict_list[secondV] = [x for x in graph_dict_list[secondV] if x != secondV ]
  # recursion
  # print (graph_dict_list)
  return contraction(graph_dict_list)

def counting(graph):
  min_cut = 0
  for i in range (5):
    # print(graph.copy()[1])
    count = contraction(graph.copy())
    if(i == 0):
      min_cut = count
    elif count < min_cut:
      min_cut = count
  return min_cut

print (counting(graph_dict))