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Union() function in Python
  • Difficulty Level : Easy
  • Last Updated : 06 Feb, 2018

Union of two given sets is the smallest set which contains all the elements of both the sets. Union of two given sets A and B is a set which consists of all the elements of A and all the elements of B such that no element is repeated.

The symbol for denoting union of sets is ‘U’

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.  


set1.union(set2, set3, set4….)
In parameters, any number of sets can be given

Return value:

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.

Below is the Python3 implementation of the above approach:

# 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))


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

Practical applications:

In most of the probability problems, the concept of union of sets is needed.

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