collections

namedtuple

定义数据类型，使数据类型更有可读性

Point = namedtuple('Point', ['x', 'y'])

# 实例化
p = Point(11, y=22)

# 像list一样访问
p[0] + p[1]

# 像dict一样方法
p.x + p.y

defaultdict

指定字典类型value的默认值

# 指定value为list
brands = collections.defaultdict(list)
for rid, brand in mget_restaurant_brands(restaurant_ids).items():
    if brand.id is None:
        continue
    brands[brand.id].append(rid)

# 指定为dict
restaurantid_foods = collections.defaultdict(dict)
for index, item in enumerate(result):
    restaurantid_foods[index][item['id']] = item['name']

# 指定为int
counter = collections.defaultdict(int)

# 可以直接进行加法运算
counter[index] += 1

OrderedDict

有序字典

class LRU(OrderedDict):
    'Limit size, evicting the least recently looked-up key when full'

    def __init__(self, maxsize=128, *args, **kwds):
        self.maxsize = maxsize
        super().__init__(*args, **kwds)

    def __getitem__(self, key):
        value = super().__getitem__(key)
        self.move_to_end(key)
        return value

    def __setitem__(self, key, value):
        super().__setitem__(key, value)
        if len(self) > self.maxsize:
            oldest = next(iter(self))
            del self[oldest]

Counter