统计列表中所有元素出现的频率

a = "i love love you you"

from collections import Counter

dict( Counter(list(a.split())) )

Out[103]: {'i': 1, 'love': 2, 'you': 2}

或者：

s = '11AAAdfdfBB'

sli = list(s.upper())

sli
Out[107]: ['1', '1', 'A', 'A', 'A', 'D', 'F', 'D', 'F', 'B', 'B']

[(i, sli.count(i)) for i in sli]
Out[108]: 
[('1', 2),
 ('1', 2),
 ('A', 3),
 ('A', 3),
 ('A', 3),
 ('D', 2),
 ('F', 2),
 ('D', 2),
 ('F', 2),
 ('B', 2),
 ('B', 2)]


sorted(sliset, key=lambda x:(-x[1]))
Out[116]: [('A', 3), ('1', 2), ('D', 2), ('F', 2), ('B', 2)]