python中的collection

'''
collection
    Counter用法
'''
import collections
words = ["hello","world","leetcode"]
chars = "welldonehoneyr"

words_cnt = collections.Counter(words)
chars_cnt = collections.Counter(chars)

print(words_cnt)
print(chars_cnt)


'''
deque:创建双向队列，可以高效实现插入和删除操作，适合用于队列和栈
append:往右添加一个元素
appenleft:往左添加一个元素 

'''
import collections
from collections import deque

words = ["hello","world","leetcode"]
words_cnt = collections.Counter(words)

queue = deque(words)
queue.append('dog')
queue.appendleft('cat')

print(queue)


"""
popleft: 获取最左边的一个元素，并在队列中删除
pop:获取最右边的元素，并在队列中删除
"""
words_left = queue.popleft()
words_right = queue.pop()

print(words_left)
print(words_right)

"""
defaultdict:当使用dict时，若key不存在，可以使用defaultdict返回一个默认值
"""
from collections import defaultdict

dd = defaultdict(lambda:'None')
dd["key1"] = '123'

print(dd["key1"])
print(dd['key2'])