First of all, my purpose is to randomly get only one element in both known sets. So my original method is firstly intersect two sets. And then randomly pick up a element from the intersected set. But this is foolish, because that I only need a elements but a intersected set.
So I need to find the algorithm of set.intersection().
I compare the cost time between the methods of 'set.intersection()' and 'for{for{}}'. Set.intersection() is more faster than other one(100 times). So using 'for{for{}}' to pick up a randomly elements is not a wise idea.
What's the algorithm behind set.intersection() in python?
The algorithm is as follows: the smaller set is looped over and every element is copied depending whether it's found in the bigger set. So, it's the C equivalent of
def intersect(a, b):
if len(a) > len(b):
a, b = b, a
c = set()
for x in a:
if x in b:
c.add(x)
return c
(Or: return set(x for x in a if x in b).)
来源：https://stackoverflow.com/questions/20100003/whats-the-algorithm-of-set-intersection-in-python