Python collections模块

官网： https://docs.python.org/3/library/collections.html#module-collections

ChainMap() 

获取多个字典的key，去掉重复

from collections import ChainMap

baseline = {'A': 'a', 'B': 'b'}
adjust = {'A': '1', 'C': '2'}
print(list(ChainMap(adjust, baseline)))  # ['A', 'B', 'C']

Counter()

统计元素出现的次数

from collections import Counter

cnt = Counter()
for word in ['red', 'blue', 'red', 'green', 'blue', 'blue', 'pink', 'black', 'red', 'yellow']:
    cnt[word] += 1
print(cnt)    # 统计出现次数  Counter({'red': 3, 'blue': 3, 'green': 1, 'pink': 1, 'black': 1, 'yellow': 1})

print(cnt.most_common(2))     # 出现次数多的前n位  [('red', 3), ('blue', 3)]

print(sorted(cnt.elements()))   # 还原 ['black', 'blue', 'blue', 'blue', 'green', 'pink', 'red', 'red', 'red', 'yellow']

c = Counter(a=3, b=2, c=1, d=0)
print(sorted(c.elements()))    # ['a', 'a', 'a', 'b', 'b', 'c']

deque()

部分方法示例。创建队列，数据在队列里的进出

from collections import deque

dq = deque('abcd')
print(dq)             # 一个队列 deque(['a', 'b', 'c', 'd'])
dq.append('x')
print(dq)            # 右端入队 deque(['a', 'b', 'c', 'd', 'x'])
dq.appendleft('y')
print(dq)            # 左端入队  deque(['y', 'a', 'b', 'c', 'd', 'x'])
dq.pop()
print(dq)            # deque(['y', 'a', 'b', 'c', 'd'])
dq.popleft()
print(dq)            # deque(['a', 'b', 'c', 'd'])
dq.rotate(1)
print(dq)            # deque(['d', 'a', 'b', 'c'])
dq.rotate(-1)
print(dq)            # deque(['a', 'b', 'c', 'd'])
dq.clear()
print(dq)            # deque([])

defaultdict()

对列表元素的各种统计

from collections import defaultdict

s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
d = defaultdict(list)
for k, v in s:
    d[k].append(v)
print(sorted(d.items()))     #  [('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]

s = 'mississippi'
d = defaultdict(int)
for k in s:
    d[k] += 1
print(sorted(d.items()))     #  [('i', 4), ('m', 1), ('p', 2), ('s', 4)]

s = [('red', 1), ('blue', 2), ('red', 3), ('blue', 1), ('red', 1), ('blue', 4)]
d = defaultdict(set)
for k, v in s:
    d[k].add(v)
print(sorted(d.items()))    #  [('blue', {1, 2, 4}), ('red', {1, 3})]

nametuple()

OrderedDict()

创建有序字典，按插入顺序

from collections import OrderedDict

d = OrderedDict.fromkeys('abcde')
print(d)              # OrderedDict([('a', None), ('b', None), ('c', None), ('d', None), ('e', None)])
d.move_to_end('b')
print(''.join(d))     # acdeb
print(d)              # OrderedDict([('a', None), ('c', None), ('d', None), ('e', None), ('b', None)])
d.move_to_end('b', last=False)
print(''.join(d))     # bacde