class Counter(dict): Counter类继承dict类、继承了dict的所有功能 计数器：
例： import collectionsobj = 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 collectionsobj = 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 collectionsobj = 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 collectionsobj = 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})