''' from collections import OrderedDict

class LastUpdatedOrderedDict(OrderedDict):

def __init__(self, capacity):
    super(LastUpdatedOrderedDict, self).__init__()
    #或者OrderedDict.__init__(self)
    #由于重写了构造方法，所以父类的构造方法不能直接继承过来
    #手动加一行：继承超(父)类构造方法
    self._capacity = capacity

def __setitem__(self, key, value):
    #instance[index]来调用这个方法
    containsKey = 1 if key in self else 0
    #如果key多于容量capacity，就pop一个
    if len(self) - containsKey >= self._capacity:
        #正是因为last=False，才先进先出
        #默认为True
        #你可以last = self.popitem()
        #remove: (3,'cool')
        last = self.popitem(last=False)
        print('remove:', last)
    if containsKey:
        del self[key]
        print('set:', (key, value))
    else:
        print('add:', (key, value))
    OrderedDict.__setitem__(self, key, value)

luod=LastUpdatedOrderedDict(3) luod[1]='short' luod[2]='rich' luod[3]='cool' luod[4]='tall' '''

输出结果 add: (1, 'short') add: (2, 'rich') add: (3, 'cool') remove: (1, 'short') add: (4, 'tall')