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

### 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 :

1. First create *two empty lists* to store the user input values.

2. Ask the user to input* total number of count* for the first list.

3. Using a loop , *take inputs for the first list.*

4. Similarly, take *total count* and take all the inputs for the *second list.*

5. 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.

6. 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 :

1. In the above example, we have fist combine both lists by using* ‘+’.*

2. Next convert the total list to a set using *‘set(list)’* method.

3. It removed all the duplicate elements . Now convert this ‘*set*‘ to a ‘*list*‘ again by using ‘*list(set)*‘ method.

4. All the *1,2 and 3 steps are written in one line.*

5. Final list is stored in variable *‘final_list’*

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