**利用列表和super实现有序字典

class MyDict(dict):
    def __init__(self):
        self.temp_list = []
        super(MyDict,self).__init__()
    def __setitem__(self, key, value):
        self.temp_list.append(key)
        super(MyDict,self).__setitem__(key, value)
    def __str__(self):
        my_list = []
        for x in self.temp_list:
            value = self.get(x)
            my_list.append("'{}':{}".format(x,value))
        temp_dict = '{'+','.join(my_list)+'}'
        return temp_dict
obj = MyDict()
obj["k1"] = 123
obj["k2"] = 456
obj["k3"] = 789
print(obj)