collections.Counter()

用于计数

from collections import  Counter

a =list(range(10))
b = Counter(a)
print(b)
a.append(1)
b = Counter(a)
print(b)
print(b[1])

结果：

Counter({0: 1, 1: 1, 2: 1, 3: 1, 4: 1, 5: 1, 6: 1, 7: 1, 8: 1, 9: 1})
Counter({1: 2, 0: 1, 2: 1, 3: 1, 4: 1, 5: 1, 6: 1, 7: 1, 8: 1, 9: 1})
2