# Python - How To Get Union of Lists in Python

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Union of lists means that all the elements from the different lists will be put up inside a single list. We can find a union of two or more than two lists. There are various methods to achieve a Union of Lists. All the methods are described below with sufficient code examples.

## Get Union of Two lists with repetition of common elements in Python

We can add two lists using the `+` operator to get the union of the two lists.

Example code:

``l1 = [1,2,3,4,5] l2 = [2,4,6.8,10]  l3 = l1 + l2  print("l1: ",l1) print("l2: ",l2) print("Union of l1 and l2 with element repetition: ",l3) ``

Output:

``l1:  [1, 2, 3, 4, 5] l2:  [2, 4, 6.8, 10] Union of l1 and l2 with element repetition:  [1, 2, 3, 4, 5, 2, 4, 6.8, 10] ``

It finds the union of the lists `l1` and `l2` and stores the result in `l3`. From the output, it is clear that we have repeated elements while finding union if we have the same element repeated in any of the list operands.

## Get Union of two List in sorted order in Python

If we wish to find the union of Lists in a sorted manner, we use the `sorted()` method to sort the list obtained after union operation.

Code :

``l1 = [11,20,1,2,3,4,5] l2 = [2,4,6,8,10]  union_l1_l2 = l1+l2 l3 = sorted(union_l1_l2)  print("l1: ",l1) print("l2: ",l2) print("Sorted union of two l1 and l2 : ",l3) ``

Output:

``l1:  [11, 20, 1, 2, 3, 4, 5] l2:  [2, 4, 6, 8, 10] Sorted union of two l1 and l2 :  [1, 2, 2, 3, 4, 4, 5, 6, 8, 10, 11, 20] ``

It computes the union of lists `l1` and `l2` using the `+` operator and stores the union in `union_l1_l2`. We use the `sorted()` method to sort the elements of the list `union_l1_l2` to get the union of `l1` and `l2` in a sorted fashion.

## Get Union of Two Lists without repetition of common elements in Python

In Python, sets are the data types that do not allow duplication of elements. So, we can use `set()` to get the union of two lists without repetition of common elements.

Code :

``def union_without_repetition(list1,list2):    result = list(set(list1 + list2))    return result  l1 = [1,2,3,4,5] l2 = [2,4,6,8,10] l3= union_without_repetition(l1,l2)  print("l1: ",l1) print("l2: ",l2) print("Union of two l1 and l2 without repetition : ",l3) ``

Output:

``l1:  [1, 2, 3, 4, 5] l2:  [2, 4, 6, 8, 10] Union of two l1 and l2 without repetition :  [1, 2, 3, 4, 5, 6, 8, 10] ``

Here, we find the union of `l1` and `l2` using the `+` operator and select only unique elements using the `set()` function and then finally convert the set into a list using the `list()` function.

## Get Union of More than Two Lists in Python

We have already computed the union of the two lists. But, what to do in the case of finding a union of more than two lists. It is very simple. We can use both the `set()` and `union()` inbuilt python function to find the union of more than two lists.

Code :

``def union(lst1, lst2, lst3):     final_list = list(set().union(lst1, lst2, lst3))     return final_list  l1 = [1,2,3,4,5] l2 = [2,4,6,8,10] l3 = [5,6,7,8,11,15,18] print("l1: ",l1) print("l2: ",l2) print("l3 : ",l3) print("Union of more than l1 l2 and l3: ",union(l1,l2,l3)) ``

Output:

``l1:  [1, 2, 3, 4, 5] l2:  [2, 4, 6, 8, 10] l3 :  [5, 6, 7, 8, 11, 15, 18] Union of more than l1 l2 and l3:  [1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 15, 18] ``

Here, we create a `set` object using `set()` constructor and then call `union()` method for the object. The `union()` method can take any number of `list` objects and return their union.

In this case, as we are using the `union()` method of the `set` class, we donâ€™t get repeated elements.