python找到多个字典中的公共键

from random import randint,sample
s = 'abcdefg'
s1 = {x:randint(1,4) for x in sample(s,randint(3,6))}
s2 = {x:randint(1,4) for x in sample(s,randint(3,6))}
s3 = {x:randint(1,4) for x in sample(s,randint(3,6))}

res = []
for k in s1:
    if k in s2 and k in s3:
        res.append(k)

s1.keys() & s2.keys() & s3.keys()

s = map(dict.keys(), [s1,s2,s3])
reduce(lambda a,b: a&b,s)