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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’
Examples:

```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.
```

Syntax:

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)) `

Output:

```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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