3. Micro:bit Iteration (Event Loop)

3.1 What is a Loop?

A loop is used to repeat code.

A common loop in MicroPython is:

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while True:

This means:

• Run the code forever
• The program keeps repeating until stopped

3.2 Basic Event Loop Example

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from microbit import *

while True:
    display.show(Image.HEART)
    sleep(500)
    display.clear()
    sleep(500)

What happens

• The program shows a heart
• Waits
• Clears the screen
• Repeats forever

3.3 How the Loop Works

Step-by-step:

1. The program enters the loop (while True)
2. Runs the code inside
3. Goes back to the top
4. Repeats again

This continues forever unless:

• The micro:bit is reset
• Power is removed

3.4 Indentation (VERY IMPORTANT)

Python uses indentation to define what belongs inside the loop.

Correct Example

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from microbit import *

while True:
    display.show(Image.HAPPY)
    sleep(1000)
    display.show(Image.SAD)
    sleep(1000)

Both images repeat because they are inside the loop

Incorrect Example

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from microbit import *

while True:
    display.show(Image.HAPPY)

sleep(1000)
display.show(Image.SAD)

What happens

• HAPPY repeats forever
• SAD never runs

3.5 Fix the Indentation

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from microbit import *

while True:
    display.show(Image.HAPPY)
    sleep(1000)
    display.show(Image.SAD)
    sleep(1000)

3.6 Using Loops with Buttons

Loops are often used to check inputs like buttons.

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from microbit import *

while True:
    if button_a.is_pressed():
        display.show(Image.YES)
    else:
        display.show(Image.NO)

What happens?

• The program constantly checks button A
• Shows different images depending on input

3.7 Combining Loops and Functions

We can call functions inside a loop.

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from microbit import *

def flash(times):
    for i in range(times):
        display.show(Image.HEART)
        sleep(200)
        display.clear()
        sleep(200)

while True:
    if button_a.is_pressed():
        flash(3)

What happens?

• The loop runs forever
• When button A is pressed → function runs

3.8 Example: Random Behaviour

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from microbit import *
import random

def random_delay():
    return random.randint(1, 3)

def show_face(delay):
    display.show(Image.HAPPY)
    sleep(delay * 1000)

while True:
    d = random_delay()
    show_face(d)

What happens?

• A random number is generated
• The display shows for a random time
• Repeats forever

3.9 Summary

Loops allow us to:

• Repeat actions continuously
• Create interactive programs
• Build event-driven systems

Key Concepts

• while True: → infinite loop
• Indentation → controls what repeats
• Functions → can run inside loops
• Inputs → (e.g. buttons) work well with loops

3.10 Practice Ideas (Micro:bit)

1. Create a loop that:

   • Flashes a smiley face continuously

2. Create a program that displays "Hello "