In this lesson we will learn how to store and interact with multiple pieces of data using lists.

Introduction to Lists

Lists order items so that they’re in a specific sequence. For example the comic strip, as a list, stores frames in a specific order. Without an order, the story wouldn’t make sense!

Lists sequences tell us that each value has a specific position in the list. The position of a value in a list is known as its **index**. We can think of an index as an address - it’s what we use to locate an item in a list.

List indices (the plural of index) are numbers. Usually, lists start their indices at 0 and then add one for each value. So if we want to select the first item in the list, we would use 0 to do so! The second item would be at index 1, and so on.

Knowing an item’s index allows us to select a value from a list and do something with it, like save it to a variable. It can also be useful in modifying a list, whether by replacing, adding, or removing something.

Let's practice modifying values in a list.


List Indices

Congratulations! Now you’ve learned about another data type known as a list.

* A list is an ordered sequence of information
* We can access an item in a list by using its index position
* We can append items to the end of the list or insert them in the middle
* We can also pop an item from the end or *remove* from the middle of a list

Lists provide us with a powerful means of storing and accessing multiple pieces of data within our programs. Next time you store a lot of information, consider using lists!

Reviewing Lists

After a list is created, we can add things to it.

When we add things to the end of an existing list, we say that we’re **appending** them to the end.

Imagine we have a list of fruit that contains `"Apples", "Bananas", and "Pears"`. When we append the value `"Mangos"`, the list would contain `"Apples", "Bananas", "Pears", and "Mangos"`. Notice how `"Mangos"` is at the end.

In addition to adding things to the end of a list, we can also insert items into the existing list. We do so by using the index number for where we want to position our new value.

Our list now contains `"Apples", "Bananas", "Pears", and "Mangos"`. Now imagine we add `"Kiwis"` at index `1`. This would add `"Kiwis"` between `"Apples"` and `"Bananas"`. After the addition, our list would contain `"Apples", "Kiwis", "Bananas", "Pears", and "Mangos"`.

It’s important to be careful - adding something in the middle of a pre-existing list, or adding it to the beginning of a list, will alter the indices for all the following items. Notice that `"Bananas"` were in the second position and are now in the third.





Adding List Elements

We’re also able to remove items from a list.

Similar to adding items, we can modify lists by taking off the last item, or we can use indexing to select a specific item and remove it from the list. Removing from the end of a list is often referred to as **pop** or **popping**.

Imagine a list of the numbers `1, 4, and 10`. Popping from this list would remove `10`, leaving `1` and `4`.

But we can also remove items from the middle of our list.
Removing from index `1` of the list `4, 7, 3` would remove `7`. This would leave `4` and `3`.



Removing List Elements

When we start writing more complex programs, we’ll start working with more pieces of data. But data can get messy real fast if we’re not careful.

To keep our data tidy, we’ll want to use data structures. Data structures are formats that we can use to keep track of our data in an organized fashion.
Lists are one very basic data structure. Programmers use lists as a container to store multiple pieces of information that relate to each other in some way. Like:

* Presidents of the US
* Types of cheeses in alphabetical order
* Finishing positions of runners in a race.

What makes lists special is that they order our data in a specific, linear sequence.

Since our values are kept in order, lists allow us to easily find the information we’re looking for; otherwise, we’d have a huge jumbled mess of data!

In this lesson, we’re going to cover:

* Accessing an item from a list
* Adding an item to a list
* Removing an item from a list
