import collections
obj = collections.Counter('aabbccc')
print(obj)#输出：Counter({'c': 3, 'a': 2, 'b': 2})

elements()

import collections
obj = collections.Counter('aabbccc')
print(sorted(obj.elements()))#输出：['a', 'a', 'b', 'b', 'c', 'c', 'c']for k in obj.elements():   #遍历打印obj所有元素print(k)``
most_common
```python
import collections
obj = collections.Counter('aabbbcccc')
print(obj.most_common(2))#输出：[('c', 4), ('b', 3)]

items()

import collections
obj = collections.Counter('aabbbcccc')
print(obj.items())for k,v in obj.items():print(k,v)#输出：dict_items([('b', 3), ('c', 4), ('a', 2)])
#     b 3
#     c 4
#     a 2

update()

import collections
obj = collections.Counter(['11','22'])
obj.update(['22','55'])
print(obj)#输出：Counter({'22': 2, '11': 1, '55': 1}

import collections
obj = collections.Counter(['11','22','33'])
obj.subtract(['22','55'])
print(obj)#输出：Counter({'11': 1, '33': 1, '22': 0, '55': -1})
``