Lists

Let’s say we have a number. Like, say, 5.

And then someone walks up to us and gives us another number. Like, say, 25.

And then they give us ten more numbers! And then ten thousand more numbers!!!

Oof, yeah, that’s a lot of numbers, we’re going to need at least a small basket. Let’s make a list of some of the numbers we have:

• 5
• 25
• 7
• 19

If you make a list of numbers using Python, it’s called… a list. That’s seriously the data type, the technical name for it! Every other programming language in all of history calls them arrays, but Python wanted to be special, so they’re called lists.

To make a list, we’ll use square brackets and commas and make something like this:

[5, 25, 7, 19]

Now it’s your turn. Make a list with three numbers: 7, 14, and 3.

• Hint: Square brackets go on the outside of the list [ to start and ] to end it
• Hint: We’ll use commas to separate the items of our list, like 1, 2, 3
• Hint: Type [7, 14, 13] and press return

What can we do with a list? I love big stuff, so I guess I’d want to know what the biggest number is.

• If len gives me the length of a string…
• …what function do you think gives me the maximum value in a list?

Hint: Think about it!

Hint: Think about it!!!

Hint: Think about it!!!!!

Yup, you use max to get the maximum value in a list. Sometimes programming is predictable! It works just like len("hello"), but with max and a list instead.

Try to use max to find the largest number in [7, 14, 3]. You’ll want to wrap the parentheses that come with max over the whoooole list.

• Hint: Your list should look like [7, 14, 3]. You’ll wrap the function max around it just like you would with something like len("hello")
• Hint: Type max([7, 14, 3]) and press enter

If you didn’t get it, no big deal — it should look like this:

max([7, 14, 3])

^{You can also do max(7, 14, 3) without the square brackets, but let’s keep that a secret!}

If max gets the maximum number in a list of numbers, can you guess the name of the function that finds the minimum number? Use it below to find the smallest number from 7, 14 and 3.

• Hint: If max gets the maximum, what gets the minimum?
• Hint: It’s min! You’ll use min the same way as max
• Hint: Type min([7, 14, 3]) and press enter

Yup, it’s min.

In the list [abs(-100) * 20, 56 * 100, abs(50 - 100) * round(2.1)], each math-y section will be converted into a number. Can you tell me what the smallest number it creates is? You’ll probably want to use cut and paste!

• Hint: You can just paste the list first if you’re curious what numbers the formulas turn into
• Hint: Use min, and cut and paste the contents of the list.
• Hint: Don’t forget the parentheses with min!
• Hint: Type min( paste [abs(-100) * 20, 56 * 100, abs(50 - 100) * round(2.1)] type ), and then press enter

There are a few more list-friendly functions I want to talk about, but first I bet you’re pretty tired of typing [7, 14, 3] again and again and again. We’ll solve that problem in the next chapter!

Chapter summary

We learned about the data type list, which you can use to make, well, lists of things. Every other language seems to call them arrays.

Have a lot of numbers? You should use a list! We haven’t talked about it yet, but you can also use lists with strings or any other data type.

We also learned a couple useful functions for lists, like max and min.