python内置模块

from collections import namedtuple
Point = namedtuple('Point',['x','y'])
p = Point(1,2)
p

Point(x=1, y=2)

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

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

from collections import OrderedDict
d = dict([('a',1),('b',2),('c',3)])
d

{'a': 1, 'b': 2, 'c': 3}

od = OrderedDict([('a', 1), ('b', 2), ('c', 3)])

od

OrderedDict([('a', 1), ('b', 2), ('c', 3)])

#OrderedDict可以实现一个FIFO（先进先出）的dict，当容量超出限制时，先删除最早添加的Key
from collections import OrderedDict
class LastUpdatedOrderedDict(OrderedDict):
    def __init__(self,capacity):
        super(LastUpdatedOrderedDict,self).__init__()
        self._capacity = capacity
    def __setitem__(self,key,value):
        containsKey = 1 if key in self else 0
        if len(self) - containsKey >= self._capacity:
            last = self.popitem(last=False)
            print("remove",last)
        if containsKey:
            del self[key]
            print('set',(key,value))
        else:
            print('add',(key,value))
        OrderedDict.__setitem__(self,key,value)
        

from collections import Counter
c = Counter()
for ch in "programming":
    c[ch] = c[ch]+1
c

Counter({'a': 1, 'g': 2, 'i': 1, 'm': 2, 'n': 1, 'o': 1, 'p': 1, 'r': 2})

import hashlib
md5 = hashlib.md5()
md5.update('how to use md5 in python hashlib?'.encode('utf-8'))
print(md5.hexdigest())

d26a53750bc40b38b65a520292f69306

import itertools
for c in itertools.chain('ABC','XYZ'):
    print(c)

A
B
C
X
Y
Z

for key,group in itertools.groupby("AAABBBCCAAA"):
    print(key,list(group))

A ['A', 'A', 'A']
B ['B', 'B', 'B']
C ['C', 'C']
A ['A', 'A', 'A']