collections模塊

一、collections

    collections模塊主要封裝了一些關於集合類的相關操作。比如，iterable，Iteratort等等，除此之外，collections還提供了一些除基本數據類型以外的數據集合類型。Counter，deque，OrderDict，defaultdict以及namedtuple

1. Counter

• 計數器，主要用來計數

from collections import Counter

s = "Hello word"
print(Counter(s))  # Counter({'l': 2, 'o': 2, 'H': 1, 'e': 1, ' ': 1, 'w': 1, 'r': 1, 'd': 1})

lst = [11, 22, 33, 44, 55, 66, 55, 44, 44]
el = Counter(lst)

print(el[44])  # 3

 2. 雙向隊列

• 既可從左邊添加數據，也可從右邊添加數據
• 既可從左邊獲取數據，也可從右邊獲取數據

from collections import deque

q = deque()

q.append(11)
q.append(22)
q.appendleft(33)

print(q)              # deque([33, 11, 22])
print(q[0])           # 33

print(q.pop())        # 22
print(q.popleft())    # 33

3. namedtuple(命名元組)

• 給元組內的元素進行命名

from collections import namedtuple

nt = namedtuple("Point", ["x", "y"])
p = nt(1, 2)

print(p.x)  # 1
print(p.y)  # 2

4. OrderedDict

• 有序字典，按照存儲的順序保存

5. defaultdict

• 給字典設置預設值。當key不存在時，直接獲取預設值
• defaultdict括弧內對象必須為可調用對象

from collections import defaultdict

dic1 = defaultdict(list)
print(dic1["name"])       # []
print(dic1)               # defaultdict(<class 'list'>, {'name': []})


def func():
    return 'Tom'

dic = defaultdict(func)
print(dic["name"])        # Tom

 應用：

# 將lst = [11, 22, 33, 44, 55, 66, 77, 88, 99]大於等於66放入字典"key1"中，小於66放入字典"key2"中
from collections import defaultdict

lst = [11, 22, 33, 44, 55, 66, 77, 88, 99]
dic = defaultdict(list)
for el in lst:
    if el < 66:
        dic["key2"].append(el)
    else:
        dic["key1"].append(el)

dic = dict(dic)
print(dic)  # {'key2': [11, 22, 33, 44, 55], 'key1': [66, 77, 88, 99]}