---
title: union
tags: list,beginner
---

Returns every element that exists in any of the two lists once.

- Create a `set` with all values of `a` and `b` and convert to a `list`.

```py
def union(a, b):
  return list(set(a + b))
```

```py
union([1, 2, 3], [4, 3, 2]) # [1,2,3,4]
```