import collections

A=['a','b','b','c','d','b','a']

count=collections.Counter(A)

print(count)

Counter({'b': 3, 'a': 2, 'c': 1, 'd': 1})

count.items()

Out[6]: dict_items([('a', 2), ('b', 3), ('c', 1), ('d', 1)])

count.keys()

Out[7]: dict_keys(['a', 'b', 'c', 'd'])

count.values()

Out[8]: dict_values([2, 3, 1, 1])

count.elements()

Out[9]: <itertools.chain at 0x7f08050d66a0>

list(count.elements())

Out[10]: ['a', 'a', 'b', 'b', 'b', 'c', 'd']

Out[20]: [1, 1, 2, 3]

sorted(count.items())

Out[21]: [('a', 2), ('b', 3), ('c', 1), ('d', 1)]

sorted(count.items(),key=lambda x:x[1])

Out[22]: [('c', 1), ('d', 1), ('a', 2), ('b', 3)]