python快速找到多个字典中的公共键

"""
第一轮:{'a': 1, 'b': 2}
第二轮:{'c': 1, 'd': 2}
... ...
统计出钱N轮，每场比赛都有进球的球员
"""

方法一：（效率低）

s = sample('abcdefg', randint(3, 6))
print s

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

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

方法二：集合操作

"""
1.使用字典的viewkeys()方法，得到一个字典keys的集合
2.使用map函数，得到所有字典的keys的集合
3.使用reduce函数，取所有的字典的keys的集合的交集
"""

s1.viewkeys()

dict_keys(['a', 'b', 'f'])

s1.viewkeys() & s2.viewkeys()

map(dict.viewkeys, [s1, s2, s3])

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