def __setitem__(self, key, value):
    super().__setitem__(key, [value] * 2) # 错误案例
class AnswerDict(dict):
  def __getitem__(self, item): # 错误案例
    return 42
import collections
class DoppelDict2(collections.UserDict): # 正确案例
  def __setitem__(self, key, value):
    super().__setitem__(key, [value] * 2)
class AnswerDict2(collections.UserDict): # 正确案例
  def __getitem__(self, item):
    return 42

class DoppelDict(dict):
  def __setitem__(self, key, value):
    super().__setitem__(key, [value] * 2)
class AnswerDict(dict):
  def __getitem__(self, item):
    return 42
import collections
class DoppelDict2(collections.UserDict):
  def __setitem__(self, key, value):
    super().__setitem__(key, [value] * 2)
class AnswerDict2(collections.UserDict):
  def __getitem__(self, item):
    return 42
class A:
  def ping(self):
    print('Ping:', self)
class B(A):
  def pong(self):
    print('pong:', self)
class C(A):
  def pong(self):
    print('PONG:', self)
class D(B, C):
  def ping(self):
    super().ping()
    print('post-ping:', self)
  def pingpong(self):
    self.ping()
    super().ping()
    self.pong()
    super().pong()
    C.pong(self)
if __name__ == '__main__':
  d = D()
  print(d.pong()) # 输出来源于B
  print(C.pong(d)) #输出来源于C 超类的方法都可以直接调用,此时要把实例作为显示参数传入.