python效率:计算dict中的键出现次数

试图获取dict密钥的唯一值以及它们出现的次数list.这有效,但感觉很笨拙:

a = [ {'pid': 1 }, {'pid': 1}, {'pid': 1}, {'pid': 2}, {'pid': 2}, {'pid': 3} ]
b = { x['pid']: len([f for f in a if f['pid'] == x['pid']]) for x in a }
b

产量:

{1: 3, 2: 2, 3: 1}

有更好的方法吗？

就在这里.用途collections.Counter:

from collections import Counter

c = Counter(d['pid'] for d in a)
print(c)
# Counter({1: 3, 2: 2, 3: 1})