limited_dict.py

# _*_ coding: utf-8 _*_
from collections import OrderedDict


class LimitedDict(OrderedDict):

    def __init__(self, limit):
        super(LimitedDict, self).__init__()
        self.limit = limit

    def __setitem__(self, key, value, dict_setitem=dict.__setitem__):
        ret = super(LimitedDict, self).__setitem__(key, value, dict_setitem)
        if len(self) > self.limit:
            self.popitem(last=False)
        return ret

if __name__ == '__main__':
    a = LimitedDict(2)
    a['a'] = 1
    a['b'] = 2
    print(repr(a))  # LimitedDict([('a', 1), ('b', 2)])

    a['c'] = 3
    print(repr(a))  # LimitedDict([('b', 2), ('c', 3)])