namedtuple

对tuple中的各个元素设定名称，并可以利用名称来访问

from collections import namedtuple, deque, defaultdict, OrderedDict

d = (1, 185, 20)
Person = namedtuple('Person', ['sex', 'tall', 'age'])

dd = Person(1, 198, 23)
print(dd)
print(dd.sex)

Output:
Person(sex=1, tall=198, age=23)
1
[Finished in 0.1s]

deque

list的插入和取出是O（n），而deque是O（1），快很多


from collections import namedtuple, deque, defaultdict, OrderedDict

q = deque([1, 2, 3])
print(q)
# 尾部插入和删除
q.append(4)
print(q)
q.pop()
print(q)
# 头部插入和删除
q.appendleft(0)
print(q)
q.popleft()
print(q)

Output:
deque([1, 2, 3])
deque([1, 2, 3, 4])
deque([1, 2, 3])
deque([0, 1, 2, 3])
deque([1, 2, 3])
[Finished in 0.1s]

Counter

统计字数

from collections import namedtuple, deque, defaultdict, OrderedDict,Counter

s = ' im happy'

re = Counter(s)
print(re)
print(re.most_common(2))

Output:
Counter({'p': 2, ' ': 2, 'h': 1, 'm': 1, 'a': 1, 'y': 1, 'i': 1})
[('p', 2), (' ', 2)]
[Finished in 0.1s]

OrderedDict

Python自带的字典是无序的，当需要有序字典时。。

from collections import namedtuple, deque, defaultdict, OrderedDict,Counter

a = (
    ('A', 1),
    ('B', 2),
    ('C', 3)
)
print(type(a))
b = dict(a)
# 注意这里的b输出顺序不是a的顺序
print(type(b))
print(b)
# 注意这里c的输出顺序与a相同
c = OrderedDict(a)
print(type(c))
print(c)

Output:
<class 'tuple'>
<class 'dict'>
{'A': 1, 'C': 3, 'B': 2}
<class 'collections.OrderedDict'>
OrderedDict([('A', 1), ('B', 2), ('C', 3)])
[Finished in 0.1s]

defaultdict

原生dict若使用dict[key]形式访问时，若指定的key不存在时，抛出KeyError错误
defaultdict中若指定key不存在，则抛出默认值:[]

from collections import namedtuple, deque, defaultdict, OrderedDict,Counter

s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]

d = defaultdict(list)

for k, v in s:
    d[k].append(v)

print(d)
print(d['blue'])
print(d['white']) # white不存在，返回[]
print(d) #此时已经将'white': [] 加入到字典

Output:
defaultdict(<class 'list'>, {'yellow': [1, 3], 'blue': [2, 4], 'red': [1]})
[2, 4]
[]
defaultdict(<class 'list'>, {'yellow': [1, 3], 'blue': [2, 4], 'white': [], 'red': [1]})
[Finished in 0.1s]