collections系列

class Counter(dict):
　　Counter类继承dict类、继承了dict的所有功能

计数器：

例：
import collections
obj = collections.Counter('sdkasdioasdjoasjdoasd')
print(obj)

得：
Counter({'s': 5, 'd': 5, 'a': 4, 'o': 3, 'j': 2, 'k': 1, 'i': 1})

拿到前几位：

""" 数量大于等n的所有元素和计数器 """

 def most_common(self, n=None):
        '''List the n most common elements and their counts from the most
        common to the least.  If n is None, then list all element counts.

        >>> Counter('abcdeabcdabcaba').most_common(3)
        [('a', 5), ('b', 4), ('c', 3)]

        '''
        # Emulate Bag.sortedByCount from Smalltalk
        if n is None:
            return sorted(self.items(), key=_itemgetter(1), reverse=True)
        return _heapq.nlargest(n, self.items(), key=_itemgetter(1))

例：
import collections
obj = collections.Counter('sdkasdioasdjoasjdoasd')
#elements　　=>> 原生的值
#obj　　　　=>> 处理完的数据
print(obj)
ret = obj.most_common(4)
print(ret)

得：

Counter({'d': 5, 's': 5, 'a': 4, 'o': 3, 'j': 2, 'k': 1, 'i': 1})
[('d', 5), ('s', 5), ('a', 4), ('o', 3)]

打印所有的元素、没有个数
for item in obj.elements():
    print(item)

dict 
otems()　　keys()　　values()

couter(dic)#继承了所有字典的方法

otems()　　keys()　　values()
“r”:3
elements()#所有的元素

for k,v in obj.items():
    print(k,v)

import collections
#obj = collections.Counter('sjhdaosdijoasjdoasd')
obj = collections.Counter(['11','22','33','22'])
print(obj)

ret = obj.most_common(4)
print(ret)

得：

Counter({'22': 2, '11': 1, '33': 1})
[('22', 2), ('11', 1), ('33', 1)]

    def update(*args, **kwds):
更新计数器，其实就是增加；如果原来没有，则新建，如果有则加一
        '''Like dict.update() but add counts instead of replacing them.

        Source can be an iterable, a dictionary, or another Counter instance.

        >>> c = Counter('which')
        >>> c.update('witch')           # add elements from another iterable
        >>> d = Counter('watch')
        >>> c.update(d)                 # add elements from another counter
        >>> c['h']                      # four 'h' in which, witch, and watch
        4

        '''
        # The regular dict.update() operation makes no sense here because the
        # replace behavior results in the some of original untouched counts
        # being mixed-in with all of the other counts for a mismash that
        # doesn't have a straight-forward interpretation in most counting
        # contexts.  Instead, we implement straight-addition.  Both the inputs
        # and outputs are allowed to contain zero and negative counts.

        if not args:
            raise TypeError("descriptor 'update' of 'Counter' object "
                            "needs an argument")
        self, *args = args
        if len(args) > 1:
            raise TypeError('expected at most 1 arguments, got %d' % len(args))
        iterable = args[0] if args else None
        if iterable is not None:
            if isinstance(iterable, Mapping):
                if self:
                    self_get = self.get
                    for elem, count in iterable.items():
                        self[elem] = count + self_get(elem, 0)
                else:
                    super(Counter, self).update(iterable) # fast path when counter is empty
            else:
                _count_elements(self, iterable)
        if kwds:
            self.update(kwds)

例（增加）：
import collections
obj = collections.Counter(['11','22','33','22'])
print(obj)

obj.update(['eric','11','11'])#增加
print(obj)

得：

Counter({'22': 2, '11': 1, '33': 1})
Counter({'11': 3, '22': 2, '33': 1, 'eric': 1})

例（减去）：
import collections
obj = collections.Counter(['11','22','33','22'])
print(obj)

obj.subtract(['eric','11','11'])#删除
print(obj)
得：

Counter({'22': 2, '11': 1, '33': 1})
Counter({'22': 2, '33': 1, '11': -1, 'eric': -1})