Example of using difference() to get all members in one set that aren't in the other set

set difference.py

# https://leetcode.com/problems/destination-city/submissions/
class Solution:
    def destCity(self, paths: List[List[str]]) -> str:
        candidates = set()
        rejects = set()
        for path in paths:
            candidates.add(path[1])
            rejects.add(path[0])
        return list(candidates.difference(rejects))[0]  # in candidates but not in rejects