1. Organising code with definitions

1.1. Definitions

Definitions help break up lengthy code into smaller well defined blocks.

Definitions start with the def keyword.
All the code for a definition is indented.
The def line ends with a colon.

Definitions use the same naming conventions as for variables.
Variable names should be in lowercase, with words separated by underscores (known as snake_case).
Variable names can only contain alphanumeric characters and underscores.
Variable cannot start with a number.

Below is an example of a definition that scrolls some text and displays an image.
The definition is run by calling it via doA().
The general rule of only using lowercase is broken here for better readability.

from microbit import *

def doA():
    display.scroll('A')
    display.show(Image.HAPPY)

doA()

1.2. Organising blocks into definitions

Compare the two code examples below.
The first example does not have any definitions.
The second example takes each block of code in the various branches of the if block and reallocates them to separate definitions.
This makes the main block of code in the while True loop more compact and more readable.
Each definition block can be easily edited and changed.

code in sequence without definitions

code organised with definitions

from microbit import *

while True:
    if button_a.is_pressed():
        display.scroll('A')
        display.show(Image.HAPPY)
    elif button_b.is_pressed():
        display.scroll('B')
        display.show(Image.SAD)
    else:
        display.scroll('C')
    sleep(1000)

from microbit import *


def doA():
    display.scroll('A')
    display.show(Image.HAPPY)


def doB():
    display.scroll('B')
    display.show(Image.SAD)


def doC():
    display.scroll('C')


while True:
    if button_a.is_pressed():
        doA()
    elif button_b.is_pressed():
        doB()
    else:
        doC()
    sleep(1000)

Side by side comparison:

Tasks

Reorganise the code below to follow the structure of the examples above.

from microbit import *

while True:
    if button_a.is_pressed():
        for char in 'ABC':
            display.scroll(char, delay=80)
    elif button_b.is_pressed():
        for sport in ['123']:
            display.scroll(sport, delay=80)
    else:
        display.clear()

Reorganise the code below to follow the structure of the examples above.

from microbit import *

while True:
    if button_a.is_pressed():
        for num in range(1, 10, 2):
            display.scroll(num, delay=80)
    elif button_b.is_pressed():
        for num in range(10, -1, -2):
            display.scroll(num, delay=80)
    else:
        display.clear()