>>> import collections

>>> obj = collections.Counter("abcde")

>>> print(obj)

Counter({'b': 1, 'a': 1, 'c': 1, 'e': 1, 'd': 1})         #分别统计每个字符出现的次数

>>> type(obj)

<class 'collections.Counter'>        #是计数器类型

>>> for k in obj.elements():

...   print(k)

...

b

a

c

e

d

>>> dic = collections.OrderedDict()

>>> type(dic)

<class 'collections.OrderedDict'>

>>> dic["k1"] = "v1"

>>> dic["k2"] = "v2"

>>> dic["k3"] = "v3"

>>> print(dic)

OrderedDict([('k1', 'v1'), ('k2', 'v2'), ('k3', 'v3')])

>>> dic.move_to_end("k1")

>>> print(dic)

OrderedDict([('k2', 'v2'), ('k3', 'v3'), ('k1', 'v1')])

>>> dic.popitem()       #按顺序删除元素，从最后一个开始

('k1', 'v1')

>>> dic.popitem()

('k3', 'v3')

>>> print(dic)

OrderedDict([('k2', 'v2'), ('k1', 'v1'), ('k3', 'v3')])

>>> dic.pop('k1')

'v1'

>>> print(dic)

OrderedDict([('k2', 'v2'), ('k3', 'v3')])

>>> dic.update({"k4":"v4"})

>>> print(dic)

OrderedDict([('k2', 'v2'), ('k3', 'v3'), ('k4', 'v4')])

>>> for i in dic.keys():         #遍历所有的key

...   print(i)

...

k2

k3

k4

>>> for i in dic.values():       #遍历所有的值

...   print(i)

...

v2

v3

v4

>>> for k,v in dic.items():     #遍历所有的键值

...   print(k,v)

...

k2 v2

k3 v3

k4 v4