python(3)-计数器，有序字典

>>> 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