Understanding Functions using the “Function Room” narrative

At the start of the program, if you use a word that’s in the red booklet, Monty will know what to do.

keywords like while, built-in functions like print, these are the things in this booklet.

When you create a variable, such as:

day = "Monday"

Monty gets an empty cardboard box, puts the string "Monday" inside the box and puts a label on the outside of the box which says day

Monty puts this box on a shelf in the Main Room

From now on, if you write day in your program, when Monty looks around the room he’ll find a box labelled day and he’ll get its contents—the string "Monday"

/2

Anyway, let’s get to defining a function:

def do_something_clever(first, second):
"""do some stuff"""
output = first + second
return output

A function is a mini-program within a program.

So, in my mental image of how computer programming works, a function is another room…

When you define a function, you’re creating a new Function Room that’s adjacent to the Main Room.

There’s a door connecting the Main Room to the Function Room.

The label on the door says do_something_clever, the name of the function.

So, when you use the name do_something_clever, Monty will look around the Main Room and see the name as a label on a door leading to another room.

If you’ve called the function by adding parentheses, do_something_clever(5, 8), Monty will open the Function Room door and go through it.

/3

However, he won’t go empty handed. He’ll take some data with him—the arguments you use when you call the function.

In the example in the previous tweet, Monty will take the integers 5 and 8 when he goes from the Main Room to the Function Room.

As Monty enters the Function Room, he’ll find two empty boxes at the entrance labelled first and second — these are the parameters from the function definition.

He’ll place the integer 5 inside the box labelled first and the integer 8 in the box labelled second. He will then place these boxes on the Function Room shelves.

Monty will then do whatever he needs to do in the Function Room.

When he’s done, he’ll return to the Main Room.

But once again, he won’t return empty-handed. He’ll take the contents of the box labelled output with him since this is what you wrote in the return statement.

Note that Monty does _not_ take the whole box labelled output with him but only its contents. In the example above, this is the integer 13

What will Monty do with this integer as he returns to the Main Room and shuts the Function Room door behind him?

If the function was called like this:

result = do_something_clever(5, 8)

then he’ll bring another empty cardboard box, place the integer 13 inside it, and label the box result. He places this box on the shelves in the Main Room.

/4