## Python 3 program to find union of two lists using set :

In this tutorial, we will learn how to find the *union of two lists using set* in Python 3. To find the union of two lists, we don’t have any built-in methods. We are going to use ’*set*’ to find the union.

### Union :

Union of two list means *it will contain all the elements of both list*. For example, if one list contains *(1,2,3,4)* and another list contains *(2,3,4,5)* then the union of both list will be *(1,2,3,4,5) .*

### Set :

Set contains only unique elements. That means no two numbers will be same.

### Algorithm to find union of two lists :

- First create
*two empty lists*to store the user input values. - Ask the user to input_ total number of count_ for the first list.
- Using a loop ,
*take inputs for the first list.* - Similarly, take
*total count*and take all the inputs for the*second list.* - Now,
*append*both lists and create one final list. This list may contain*duplicate numbers*. Convert this list to a ’*set*’ to remove the duplicate numbers. - Finally, Convert the
*‘set’ to a ‘list’*and print out the result.

### Python 3 program :

```
first_list = []
second_list = []
#get total count for the first list
count_first_list = int(input("Enter total numbers of the first list : "))
#take inputs from the user for the first list
for i in range(1,count_first_list+1):
no = int(input("Enter : "))
first_list.append(no)
#get total count for the second list
count_second_list = int(input("Enter total numbers of the second list : "))
#take inputs from the user for the second list
for i in range(1,count_second_list+1):
no = int(input("Enter : "))
second_list.append(no)
#print first and second list
print("First list : ",first_list)
print("Second list : ",second_list)
#find union of both list
final_list = list(set(first_list + second_list))
#print the final list
print("Final list : ",final_list)
```

### Sample Output :

```
Enter total numbers of the first list : 3
Enter : 1
Enter : 2
Enter : 3
Enter total numbers of the second list : 3
Enter : 2
Enter : 3
Enter : 4
First list : [1, 2, 3]
Second list : [2, 3, 4]
Final list : [1, 2, 3, 4]
```

### Explanation :

- In the above example, we have fist combine both lists by using_ ’+’._
- Next convert the total list to a set using
*‘set(list)’*method. - It removed all the duplicate elements . Now convert this ’
*set*’ to a ’*list*’ again by using ’*list(set)*’ method. - All the
*1,2 and 3 steps are written in one line.* - Final list is stored in variable
*‘final*list’_

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