First Program

In general, the process of designing code is composed of these 4 steps. You can expect to go around the loop quite a few times before you get your code working.


Design the Code

First of all you are going to write a program to display the message “Hello UCL!” followed by an image on the display of your micro:bit and print “Hi there” to Mu console. It’s a good practice to think about what you want your code to do and how you’re going to do it before you start writing. There’s not much planning and design to do here, but just so that you understand what a plan might look like:

Repeat forever:
    Scroll "Hello UCL!" across the LED display
    Display a heart icon
    Print "Hello World!" on a console
    Delay for 2 seconds

There are two ways to display the output of your code: you either use outputs available on the micro:bit (eg. the LEDs) or the REPL (Read Print Evaluate Loop) console available in the editor using the print statement. The console is especially useful for finding bugs (errors) in your code or trying out new concepts or ideas.

Let’s go through this line-by-line:

from microbit import *

Importing packages (like microbit) in Python makes us able to use functions or objects which are not defined in pure Python. In this case it’s for example display or show.

while True:

This means do something (whatever follows this statement and is indented) while the condition following while is true. In this case, the condition is the keyword True, means that this loop will go on forever - it’s the same as writing (5 > 1), which evaluates to True in the end anyway. The rest of the program is straightforward:

from microbit import *

while True:'Hello UCL!')
        print('Hello World!')

This displays Hello UCL! on the LED display and then shows the heart. The statement print('Hi There!!'), will print the message in the REPL. Press the REPL button in the menu now to show the REPL window:


The REPL window shows us messages from the micro:bit and also allows us to send commands directly to the micro:bit. For now, we’ll just be using the REPL to see messages that we print and error messages.

Upload your program

Now click on the Flash button in Mu and see what happens.


The result on the micro:bit should look something like this:


Now try to open the REPL console:


Make a change

The best way to learn what something is for is to try and change your code (and read the documentation, obviously).


Are you wondering what the delay is for? Is it necessary? Try deleting it. What happens if you replace True by False? What happens when you replace scroll by show?

Now you have written your first program. Next sections will tell you more about writing more complex programms and about further uses of micro:bit.

See also

See the full micro:bit documentation for MicroPython.