What you'll learn

Importing a module of your own
Putting reusable code in a separate file
Calling a function from another file
Making random numbers with the random module

Difficulty: Beginner
Time: About 10 minutes
Board: Raspberry Pi Pico
Parts: 1

How it works

This project has two files. helpers.py holds a small function called pick. main.py does import helpers and calls it. MicroPython finds helpers.py on the board's filesystem, next to main.py.

Every second the loop prints a random number between 1 and 100. Nothing is wired. Splitting code into modules keeps bigger programs tidy.

Parts list

1 part, plus the jumper wires. They retail for about $4; on Mokxi they're free.

1 × Raspberry Pi PicoIn Fight Stick Kit.

Kits that can build it

These 4 starter kits have every part in the circuit. Each kit's page lists what else it can build.

The code

The MicroPython code exactly as the editor opens it. Change a line there and press Run: the board runs it on the official MicroPython firmware, with nothing to compile.

main.py · Raspberry Pi Pico

# Your own module: helpers.py is in the next tab. import finds it on the
# board's filesystem, next to main.py, the same way it finds machine.
import time
import helpers

while True:
    print("random number:", helpers.pick(1, 100))
    time.sleep(1)

helpers.py · Raspberry Pi Pico

# helpers.py: a module of your own. main.py imports it and calls pick().
import random

def pick(low, high):
    """A whole number from low to high, both included."""
    return random.randint(low, high)

Code walkthrough

The key functions of the sketch, and what each one does.

`pick` helpers.py

Lives in helpers.py. It takes low and high and returns random.randint(low, high), a whole number that can be either end. main.py calls helpers.pick(1, 100) to get a number from 1 to 100.

def pick(low, high):
    """A whole number from low to high, both included."""
    return random.randint(low, high)

Troubleshooting

The usual mistakes with this circuit, and the fix for each.

ImportError: no module named helpers This project
The file must be called helpers.py and sit next to main.py. Check the spelling of the name in import helpers.
The Pico does not show up as a drive, or the program will not load. Raspberry Pi Pico
Hold the BOOTSEL button while you plug in USB. A drive named RPI-RP2 appears. Then copy the UF2 file onto it.
A 5 V signal or sensor is wired to a GPIO pin. Raspberry Pi Pico
Pico GPIO pins are 3.3 V only and are not 5 V tolerant. Use a level shifter or a voltage divider for any 5 V output going into the board.