执行dict [k]时，由dict.keys（）返回的密钥k导致KeyError：现有密钥上的KeyError

以下代码

for k in list(g_score.keys()):
    print(g_score[k])

KeyError为我返回一个：

Traceback (most recent call last):
  File "./np.py", line 134, in <module>
    main()
  File "./np.py", line 131, in main
    NPuzzle(n).solve()
  File "./np.py", line 116, in solve
    print(g_score[k])
KeyError: 3

我不知道什么时候print(list(g_score.keys()))是可能的[4, 3, 7]。3显然在字典中。

对于上下文，我正在尝试对N-Puzzle问题实施A *搜索（并且我什至不确定A *是否正确实施，因为我无法克服此错误），并具有以下State类和solve功能：

class State:
    def __init__(self, blank_idx, puzzle, g=0, h=0):
        self.blank_idx = blank_idx
        self.puzzle = puzzle
        self.f = g + h

    def __eq__(self, other):
        return self.puzzle == other.puzzle

    def __hash__(self):
        return self.f + self.blank_idx

    def __lt__(self, other):
        return self.f < other.f

    def __repr__(self):
        return str(self.f)

...

class NPuzzle:

    # ...other stuff

    def solve(self):
      start_state = State(
          self.puzzle.index(' '),
          self.puzzle,
          0,
          self.cost(self.puzzle)
      )

      g_score = {start_state: 0}
      open_set = [start_state]
      path = {}

      while open_set:
          state = open_set[0]

          if state.puzzle == self.goal_state:
              break

          heappop(open_set)
          for next_state in self.neighbors(state):
              g = g_score[state] + 1
              if next_state in g_score and g >= g_score[next_state]:
                  continue

              path[next_state] = state
              g_score[next_state] = g
              next_state.f = g + self.cost(next_state.puzzle)
              heappush(open_set, next_state)

我首先在我所在的行上遇到了错误：

g = g_score[state] + 1

我不确定为什么会这样KeyError，但是我假设这可能与我的自定义__hash()__函数有关。