> a = [1,2,3]
> b=[1,2]
> ####################################
> #两个列表的差集
> ret = []
> for i in a:
  if i not in b:
     ret.append(i)
 
> ret
[3]
> #两个列表的差集2
> ret2 = [ i for i in a if i not in b ]
> ret2
[3]
> #两个列表的差集3
> ret3 = list(set(a) ^ set(b))
> ret3
[3]
> #两个列表的差集4
> ret4=list(set(a).difference(set(b))) # b中有而a中没有的
> ret4
[3]

> ########################################
> #获取两个list 的并集
> ret1=list(set(a).union(set(b)))
> ret1
[1, 2, 3]
> ret1=list(set(a).union(set([4,5,6])))
> ret1
[1, 2, 3, 4, 5, 6]
> #获取两个list 的并集2
> ret2= list(set(a) | set(b))
> ret2
[1, 2, 3]
> ret2=list(set(a)-set(b))#####差集
> ret2
[3]

> ##########################################
> #获取两个列表的交集
> a = [1, 2, 3, 4, 5, 6]
> b = [2, 4, 6, 8 ,10]
> ret1= [x for x in b if x in set(a)]  # list a is the larger list b
> ret1
[2, 4, 6]
> #获取两个列表的交集2
> ret2= list(set(a) & set(b))
> ret2
[2, 4, 6]
> #获取两个列表的交集3
> ret3= list(set(a).intersection(b))
> ret3
[2, 4, 6]
> #获取两个列表的交集4
> ret4 = list((set(a).union(set(b)))^(set(a)^set(b)))
> ret4
[2, 4, 6]
>