# Everything about Python Set

This post intends to teach you everything about Pythonâ€™s set. Honestly, I hope you can learn here how useful this statement can be, I think sets are the most underrated data structure in python. The post targets in showing you how to use the main set operations: add, remove, union, intersection, set to list, etc

## 1. Defining a Set

In python, a set is a collection of unique values that are unordered and unindexed which are defined by curly brackets.

```>>> my_set = {"San Diego", "New York", "Santa Barbara", "Miami"}
>>> my_set
>>> {'San Diego', 'New York', 'Miami', 'Santa Barbara'}
```

Clearly, as you can see above, the set came out unordered. Thus, a list structure should be used if the order of the elements matters to you.

Also, Sets store unique values, if we define a set with a repeated value, then only one representation of the value will be stored.

Despite being defined twice in the set, the city “New York” only shows once.

```>>> my_set = {"San Diego", "New York", "Santa Barbara", "Miami", "New York"}
>>> my_set
>>> {'San Diego', 'Miami', 'New York', 'Santa Barbara'}
```

Moreover, you can remove repeated items from a list by converting it to a set and then back to s list.

```>>> my_list = [1, 1, 1, 1, 1, 2, 2, 3, 3, 1, 3, 3]
>>> new_list = list(set(my_list))
>>> new_list
>>> [1, 2, 3]
```

An application for this is on removing repeated DNA sequences for a large file.

## 2. Add an Item to a Set

Adding an element to a set is simple can be accomplished by calling add() in a set that was already initiated.

```>>> my_set = {"San Diego", "New York", "Santa Barbara", "Miami"}
>>> # add the string "Dallas" to set
>>> my_set
>>> # as you can see, "Dallas" was added to set
>>> {'San Diego', 'Dallas', 'New York', 'Miami', 'Santa Barbara'}
```

## 3. Remove an Item to a Set

An item is removed from a set by entering the target item to the method remove() or discard().

```>>> my_set = {"San Diego", "New York", "Santa Barbara", "Miami"}
>>> my_set.remove("Miami")
>>> my_set
>>> # remove "Miami" from set
>>> {'San Diego', 'New York', 'Santa Barbara'}
```

## 4. Merging – Union Two sets

Sets are merged (union) by calling the method union() which requires another set as a parameter.

```>>> my_set = {"San Diego", "New York"}
>>> my_set_2 = {"Santa Barbara", "Miami"}
>>> my_set_3 = my_set.union(my_set_2)
>>> my_set_3
>>> {'San Diego', 'Miami', 'New York', 'Santa Barbara'}
```

In conclusion, I hope you see why a set is the most underrated data structure. Furthermore, I hope this tutorial taught you some lessons on how to use the set statement on Python. Please comment below if there is anything else you would love to learn.

## 5. Set intersection

You can find the set intersection with another set(s) by using the method intersection() which requires another set as a parameter.

```>>> my_set = {"San Diego", "New York"}
>>> my_set_2 = {"San Diego", "Santa Barbara", "Miami"}
>>> my_intersection = my_set.intersection(my_set_2)
>>> my_intersection
>>> {"San Diego"}
```

If you have more than one set, you can do it as the following:

```>>> my_set = {"San Diego", "New York"}
>>> my_set_2 = {"San Diego", "Santa Barbara", "Miami"}
>>> my_set_3 = {"San Diego", "Miami"}
>>> my_intersection = my_set.intersection(my_set_2, my_set_3)
>>> my_intersection
>>> {"San Diego"}
```

## 6. Set to list

It is simple to convert a set to a list – just call the function list() and pass a set.

```>>> my_set = {"San Diego", "New York"}
>>> my_list_from_set = list(my_set)
>>> my_list_from_set
>>> ["San Diego", "New York"]
>>> type(my_list_from_set)
>>> <class 'list'>
```

## More Resources

Here are three of my favorite Python Books in case you want to learn more about it.