快速查找字典中的公共键

举例

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在三个字典中找出都存在的键

一般方法

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从一个字典中依次遍历键，然后判断其余两个字典是否存在这个键。代码如下：

from random import randit, sample

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))}

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

sample是一个随机采样函数

这样做逻辑上比较简单，但是效率不高

使用集合的方式

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首先使用viewkeys()的方法，得到一个字典，然后分别用map和reduce函数得到所有字典键的集合和所有集合的交集。代码如下：

字典个数比较少的情况下

from random import randit, sample

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))}

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

当字典个数比较多的情况下

假设要求n个字典的公共键的集合，代码如下：

from random import randit, sample

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))}

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