python第三天---collections类

collection系列

1.计数器（counter）

Counter是对字典类型的补充，用于追踪值的出现次数。

我们从中挑选一些相对常用的方法来举例：

在上面的例子我们可以看出，counter方法返回的是一个字典，它将字符串中出现的所有字符都进行了统计。在这里再介绍一下update方法，这个update方法是将两次统计的结果相加，和字典的update略有不同。

2.有序字典（OrderedDict）：

orderdDict是对字典类型的补充，主要是可以按照字典元素添加顺序输出。

普通字典：无序的，它依靠key，value之间的索引进行匹配。

 dict={　　　　　　　　　　　　　　　　　　　　　　

     '':'test1',

     '':'test2',

     '':'test3',

     '':'test4',

     '':'test5',

     '':'test6'

 }

 for k,v in dict.items():

     print k,v

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有序字典：字典在内部自动维护了一个key列表。

import collections

dict1=collections.OrderedDict()

for lines in range(1,7):

    dict1[str(lines)]='test%s'%(lines)

for k,v in dict1.items():

    print k,v

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3.默认字典（defaultdict）

defaultdict是对字典的类型的补充，他默认给字典的值设置了一个类型。

有如下值集合 [11,22,33,44,55,66,77,88,99,90...]，将所有大于 66 的值保存至字典的第一个key中，将小于 66 的值保存至第二个key的值中。

即： {'k1': 大于66 , 'k2': 小于66}

常用方法：

dic={}

li=[11,22,33,44,55,66,77,88,99]

for item in li:

    if item>66:

        if 'k2'in dic.keys():

            dic['k2'].append(item)

        else:

            dic['k2']=[item,]

     else:

        if 'k1' in dic.keys():

            dic['k1'].append(item)

        else:

            dic['k1']=[item

用默认字典实现

 import collections

 value=[11,22,33,44,55,66,77,88,99]

 dict1=collections.defaultdict(list)

 for list1 in value:

     if list1<=66:

         dict1['k1'].append(list1)

     else:

         dict1['k2'].append(list1)

 print dict1

4、可命名元组(namedtuple)

根据nametuple可以创建一个包含tuple所有功能以及其他功能的类型：

主要用于‘坐标’的表示。用法如下：

 import collections as coll

 >>> mytuple=coll.namedtuple('mytuple',['x','y'])

 >>> n=mytuple(1,2)

 >>> n

 mytuple(x=1, y=2)

 >>> n.x

 1

 >>> n.y

 2

5、双向队列(deque)

一个线程安全的双向队列：双向队列我们可以理解为两个栈底相连的栈，和队列的先进先出不同，元素可以从这个队列的两端分别加入或者删除值。

 a=coll.deque()

 a.append(1)

 a.append(2)

 a.append(3)

 print a.pop()

 3

 print a.popleft()

 1