# 2.3.4. Interaction Between 2 Lists#

## 2.3.4.1. set.union: Find the Union of Two Sets#

To obtain all unique elements from two lists, convert the lists to sets and then use the `set.union` method to find the union of the two sets.

```requirement1 = ['pandas', 'numpy', 'statsmodel']
requirement2 = ['numpy', 'statsmodel', 'matplotlib']

set(requirement1).union(set(requirement2))
```
```{'matplotlib', 'numpy', 'pandas', 'statsmodel'}
```

## 2.3.4.2. set.intersection: Find the Intersection Between Two Sets#

To get the common elements between two lists, convert the lists to sets then use the `set.intersection` method to find the intersection between two sets.

```intersection = set(requirement1).intersection(set(requirement2))
list(intersection)
```
```['statsmodel', 'numpy']
```

## 2.3.4.3. Set Difference: Find the Difference Between Two Sets#

To find the difference between 2 lists, turn those lists into sets then apply the `difference()` method to the sets.

```# Find elements in requirement1 but not in requirement2
diff = set(requirement1).difference(set(requirement2))
print(list(diff))
```
```['pandas']
```
```# Find elements in requirement2 but not in requirement1
diff = set(requirement2).difference(set(requirement1))
print(list(diff))
```
```['matplotlib']
```