参考链接： Python Set union()

两个给定集合的并集是包含两个集合的所有元素的最小集合。两个给定集合A和B的并集是一个由A的所有元素和B的所有元素组成的集合，这样就不会重复任何元素。

 表示集合并集的符号是“ U”。示例：

 Input:Let set A = {2, 4, 5, 6}

 and set B = {4, 6, 7, 8}

 Output:{2, 4, 5, 6, 7, 8}

 Explanation:Taking every element of both the sets A and B,

 without repeating any element, we get a

 new set = {2, 4, 5, 6, 7, 8}.This new set

 contains all the elements of set A and all the elements

 of set B with no repetition of elements and is

 named as union of set A and B.

 用法:

 set1.union(set2, set3, set4….)

 In parameters, any number of sets can be given

 返回值：

 The union() function returns a set, which has the union of all sets(set1, set2, set3…) with set1.

 It returns a copy of set1 only if no parameter is passed.

 以下是上述方法的Python3实现：

 # Python3 program for union() function

 set1 = {2, 4, 5, 6}

 set2 = {4, 6, 7, 8}

 set3 = {7, 8, 9, 10}

 # union of two sets

 print("set1 U set2:", set1.union(set2))

 # union of three sets

 print("set1 U set2 U set3:", set1.union(set2, set3))

 输出：

 set1 U set2: {2, 4, 5, 6, 7, 8}

 set1 U set2 U set3:{2, 4, 5, 6, 7, 8, 9, 10}

 实际应用：

 在大多数概率问题中，需要集合并集的概念。