python collections模块

在内置数据类型（dict、list、set、tuple）的基础上，collections模块还提供了几个额外的数据类型：Counter、deque、defaultdict、namedtuple和OrderedDict等。

1.namedtuple: 生成可以使用名字来访问元素内容的tuple

import collections
name_tuple = collections.namedtuple("birthday", ["Year", "Month", "Day", "Hour", "Minute"])
new_tuple = name_tuple("1990","12","22","4","35")
print(new_tuple)
print(new_tuple.Day)

结果对照:

birthday(Year='1990', Month='12', Day='22', Hour='4', Minute='35')
22

2.deque: 双向队列，可以快速的从另外一侧追加和推出对象

from collections import deque
q = deque(['a', 'b', 'c'])
q.append('x')
q.appendleft('y')
print(q)

q.pop()
q.popleft()
print(q)

结果对照:

deque(['y', 'a', 'b', 'c', 'x'])
deque(['a', 'b', 'c'])

3.defaultdict: 带有默认值的字典

from collections import defaultdict
dd = defaultdict(lambda: 'N/A')     # 使用dict时，如果引用的Key不存在，就会抛出KeyError。如果希望key不存在时，返回一个默认值
dd['key1'] = 'abc'
print(dd['key1']) # key1存在

print(dd['key2']) # key2不存在，返回默认值

结果对照:

abc
N/A

from collections import defaultdict
values = [11, 22, 33,44,55,66,77,88,99,90]
my_dict = defaultdict(list)

for value in  values:
    if value>66:
        my_dict['k1'].append(value)
    else:
        my_dict['k2'].append(value)

print(my_dict)

结果对照:

defaultdict(<class 'list'>, {'k2': [11, 22, 33, 44, 55, 66], 'k1': [77, 88, 99, 90]})

3.Counter: 计数器，主要用来计数,返回字典形式

from collections import Counter
c = Counter('abcdeabcdabcaba')
print(c)

结果对照:

Counter({'a': 5, 'b': 4, 'c': 3, 'd': 2, 'e': 1})