[python] 집합 Sets

S1 = set( L1 )
S2 = set( L2 )

맴버쉽 테스트
item in S1

차집합
S1 - S2

합집합
S1 | S2

교집합
S1 & S2

elements in S1 or S2 but not both
S1 ^ S2