# 建立相同公共鍵字典

from random import randint,sample

sample('abcdefg',randint(3,6))

s1 = {k:randint(1,4) for k in sample('abcdefg',randint(3,6)) }

s2 = {k:randint(1,4) for k in sample('abcdefg',randint(3,6)) }

s3 = {k:randint(1,4) for k in sample('abcdefg',randint(3,6)) }

# 提取字典中公共鍵第一種方法：

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

# 第二種方法：使用字典的viewkeys()方法得到一個字典keys的集合

    s1.viewkeys() & s2.viewkeys() & s3.viewkeys()


# 第三種方法：（1）使使用map函式得到所有字典的keys的集合

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

# （2）使用reduce函式，取所有字典keys的集合的交集
    reduce(lambda a,b :a & b,map(dict.viewkeys,[s1,s2,s3]))