# Understanding Functions using the "Function Room" narrative
I use narratives to learn stuff… and to teach, too
What's a narrative? It's a way of connecting events or facts in a form of a story
But I promised to talk about The **Function Room**…
so read on…
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My mental image of a computer program is that of a small creature working in a room.
When you start writing a program, the Main Room is empty except for some shelves and a small red booklet called "built-in"
Monty — that's the name of the little creature doing all the hard work — will look around the room whenever you use any name.
_more in the next toot_
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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.
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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.
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However, if the function call was just:
`do_something_clever(5, 8)`
then Monty doesn't know what to do with the data he's holding. So he'll throw it away in the garbage bin so he can carry on with his work.
What if you write:
`print(do_something_clever(5, 8))`
Monty will go to the `do_something_clever` Function Room, do what he needs to do, and return to the Main Room holding the integer `13`…
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…but he won't stay there long. Monty finds the name `print` in the built-in red booklet which gives him directions to the `print` Function Room which is elsewhere in Python City.
He'll leave the Main Room to go to the `print` Function Room, taking the integer `13` with him.
When Monty finishes from the `print` Function Room, he'll return to the Main Room and carry on with whatever instructions come next.
Usual caveat: analogies are not perfect. So don't take them literally. Literally!
But, our brains react better to narratives rather than random facts. So I find that these 'stories' help me understand and remember this stuff so much better…
Hopefully it will help others, too.
If you want to read more on this analogy, you can read this:
https://thepythoncodingbook.com/understanding-programming-the-white-room/
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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"`
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