Functions and Flowers

By the end of this lesson you'll be able to:

• Define your own function with def and call it by name
• Call a function multiple times from inside a loop
• Build a flower drawing by repeating a petal() function

What if you could give a chunk of code a name and run it whenever you want — just by saying the name? That's what a function is. In this lab you'll define a petal() function and call it in a loop to grow a full flower on the canvas.

Welcome to This Lesson!

Functions are the secret to writing code that's short, clear, and easy to reuse. Today we're going to grow a flower together — one petal at a time! Let's code it together!

Defining a Function

A function is a block of code you write once and can run as many times as you want by calling its name. You create one with def:

def petal():
    monty.forward(100)
    monty.right(120)
    monty.forward(100)
    monty.right(120)
    monty.forward(100)
    monty.right(120)

This function draws one triangle — one petal. To use it, call petal(). To draw four petals, call it four times (or put it in a loop).

Scratch Bridge

In Scratch you used "My Blocks" to define a custom block and then drag it where you needed it. In Python, def petal(): defines the block, and petal() is how you use it — every time you call it, the whole function runs!

Sample Code

import turtle
monty = turtle.Turtle()
monty.shape('turtle')

distance = 80
angle = 120

def petal():
    monty.begin_fill()
    monty.color('pink')
    for i in range(3):
        monty.forward(distance)
        monty.right(angle)
    monty.end_fill()
    monty.right(90)

for i in range(4):
    petal()

monty.pensize(6)
monty.color('green')
monty.right(45)
monty.forward(120)
monty.hideturtle()

What Do You Think Will Happen?

petal() is called 4 times, and each petal rotates 90 degrees from the last. What do you think the full drawing will look like — a flower, a pinwheel, something else? Make your guess — then click Run!

Try It Now

Edit the code below and click Run to see the result right on this page. No account needed — everything runs in your browser.

▶ Run ↻ Reset

Were you right? Four filled pink triangles arranged around a center with a green stem — a flower!

How It Works

def petal(): creates the function but doesn't run it yet. The code inside it stays idle until you call petal(). When the for i in range(4): loop runs, it calls petal() four times. Each call draws one triangle and then rotates the turtle 90 degrees so the next petal points in a new direction.

begin_fill() and end_fill() paint the inside of whatever shape the turtle traces between those two calls. hideturtle() removes the turtle cursor at the end for a cleaner result.

Explanation Table

Line	What it does
def petal():	Defines a function called petal — code here runs when petal() is called
monty.begin_fill()	Starts recording the path for filling
monty.color('pink')	Sets the fill and outline color to pink
for i in range(3):	Loops 3 times inside the function to draw each triangle side
monty.end_fill()	Fills the enclosed area with the current color
monty.right(90)	Rotates 90° so the next petal faces a new direction
for i in range(4): petal()	Calls the function 4 times to draw 4 petals

Learning Check

Spot the Bug!

The program below tries to draw 4 petals, but only one appears before the program stops. The function is never called inside the loop. Can you find and fix the problem?

▶ Run ↻ Reset

Experiments

Try these changes to the flower code. Predict first, then run!

1. Change monty.color('pink') to monty.color('yellow'). You'll know it worked when the petals are yellow instead of pink.

2. Change for i in range(4): petal() to for i in range(6): petal() and the rotation inside petal to monty.right(60). You'll know it worked when you see 6 petals instead of 4.

3. Change distance = 80 to distance = 120. You'll know it worked when the petals are noticeably larger.

4. Add an if/else inside petal() so it alternates between 'pink' and 'purple' using i % 2. You'll know it worked when the petals alternate colors. (Hint: you'll need to pass i to the function.)

5. Change the stem direction: replace monty.right(45) with monty.left(45). You'll know it worked when the stem grows upward-left instead of downward-right.

Great Work!

You defined your first function and used it to build something beautiful! In the next lab you'll give your functions parameters so the same function can draw different things depending on what you pass in. Let's code it together!