YCL Session 4 You put the fun in functions! Functions A function is - - PowerPoint PPT Presentation

YCL Session 4 You put the ’fun’ in functions!

Functions

A function is a block of code that we can call with just one line. Functions give us the ability to write:

• Clear, easy-to-read code.
• The ability to reuse that code.

Function Anatomy

To create our own drawing functions we need three things, the latter two which which we learned in our last session:

• 1. How to define a function
• 2. How to use variables
• 3. How to create simple mathematical expressions

Step 1: Defining

• 5. A colon
• 6. Include 4 spaces or a tab
• 7. Then the meat of your

functions!

• 1. Comment: what does this

function do?

• 2. Use def
• 3. Then name the function
• 4. Parentheses

Example

def draw_grass(): """ This function draws the grass. """ arcade.draw_lrtb_rectangle_filled(0, 800, 200, 0, arcade.color.BITTER_LIME)

Step 2: Calling

Our computer needs to know when it should use the function we’ve just defined. To do so, just use the name of the function: draw_grass()

grass.py

1.

Create a new directory Session 4 in PyCharm

2.

Create a new file under Session 4

3.

Call it grass.py

4.

See the Code Snippet called grass.pdf

5.

Copy and paste

6.

Run!

tree.py

• 1. Create a new file under Session 4
• 2. Call it tree.py
• 3. See Code Snippet called grass.pdf
• 4. Copy and paste
• 5. Run!

Step 3: Using Expressions

forest.py

• 1. Create a new file under Session 4
• 2. Call it forest.py
• 3. See Code Snippet called grass.pdf
• 4. Copy and paste
• 5. Run!

Cylinder Volume

Function that returns the volume of a cylinder def volume_cylinder(radius, height): pi = 3.141592653589 volume = pi * radius ** 2 * height return volume Because of the return, this function could be used later on as part of an equation to calculate the volume of a six-pack like this: six_pack_volume = volume_cylinder(2.5, 5) * 6

Capturing Values

Functions can take in AND return values, as in the cylinder example BUT be careful: seeing it in the code and seeing the

• utput is not the same!

We need to “capture” the returned value in a new variable, and then print that variable outside of the function in order to see it.

Variable Scope

# Define a simple function that sets x equal to 22 def f(): x = 22 # Calling the function works f() # This fails because x only exists in f() print(x)

functions.py

1.

Create a new file under Session 4

2.

Call it functions.py

3.

See Code Snippets for reference, and Activity for Instructions

4.

Use Session 2 drawing for inspiration!