One of the best things about CircuitPython is how simple it is to get code up and running. This section covers how to create and edit your first CircuitPython program.

To create and edit code, all you'll need is an editor. There are many options.Adafruit strongly recommends using Mu! It's designed for CircuitPython, and it's really simple and easy to use, with a built in serial console!

If you don't or can't use Mu, there are a number of other editors that work quite well. TheRecommended Editors page has more details. Otherwise, make sure you do "Eject" or "Safe Remove" on Windows or "sync" on Linux after writing a file if you aren't using Mu. (This was formerly not a problem on macOS, but see the warning below.)

Creating Code

Copy and paste the following code into your editor:

import boardimport digitalioimport timeled = digitalio.DigitalInOut(board.LED)led.direction = digitalio.Direction.OUTPUTwhile True:    led.value = True    time.sleep(0.5)    led.value = False    time.sleep(0.5)

import boardimport digitalioimport timeled = digitalio.DigitalInOut(board.LED)led.direction = digitalio.Direction.OUTPUTwhile True:    led.value = True    time.sleep(0.5)    led.value = False    time.sleep(0.5)

If you're using a KB2040, QT Py, Quaila, or a Trinkey, or any other board without a single-color LED that can blink, please download theNeoPixel blink example.

The little LED should now be blinking. Once per half-second.

Congratulations, you've just run your first CircuitPython program!

Editing Code

Your code changes are run as soon as the file is done saving.

There's one warning before you continue...

The CircuitPython code on your board detects when the files are changed or written and will automatically re-start your code. This makes coding very fast because you save, and it re-runs. If you unplug or reset the board before your computer finishes writing the file to your board, you can corrupt the drive. If this happens, you may lose the code you've written, so it's important to backup your code to your computer regularly.

There are a couple of ways to avoid filesystem corruption.

1. Use an editor that writes out the file completely when you save it.

Check out theRecommended Editors page for details on different editing options.

2. Eject or Sync the Drive After Writing

If you are using one of our not-recommended-editors, not all is lost! You can still make it work.

On Windows, you can Eject or Safe Remove theCIRCUITPYdrive. It won't actually eject, but it will force the operating system to save your file to disk. On Linux, use thesync command in a terminal to force the write to disk.

You also need to do this if you use Windows Explorer or a Linux graphical file manager to drag a file ontoCIRCUITPY.

import supervisorsupervisor.runtime.autoreload = False

import supervisorsupervisor.runtime.autoreload = False

Back to Editing Code...

Now! Let's try editing the program you added to your board. Open yourcode.py file into your editor. You'll make a simple change. Change the first0.5 to0.1. The code should look like this:

import boardimport digitalioimport timeled = digitalio.DigitalInOut(board.LED)led.direction = digitalio.Direction.OUTPUTwhile True:    led.value = True    time.sleep(0.1)    led.value = False    time.sleep(0.5)

import boardimport digitalioimport timeled = digitalio.DigitalInOut(board.LED)led.direction = digitalio.Direction.OUTPUTwhile True:    led.value = True    time.sleep(0.1)    led.value = False    time.sleep(0.5)

Leave the rest of the code as-is. Save your file. See what happens to the LED on your board? Something changed! Do you know why?

You don't have to stop there! Let's keep going. Change the second0.5 to0.1 so it looks like this:

while True:    led.value = True    time.sleep(0.1)    led.value = False    time.sleep(0.1)

while True:    led.value = True    time.sleep(0.1)    led.value = False    time.sleep(0.1)

Now it blinks really fast! You decreased the both time that the code leaves the LED on and off!

Now try increasing both of the0.1 to1. Your LED will blink much more slowly because you've increased the amount of time that the LED is turned on and off.

Well done! You're doing great! You're ready to start into new examples and edit them to see what happens! These were simple changes, but major changes are done using the same process. Make your desired change, save it, and get the results. That's really all there is to it!

Naming Your Program File

CircuitPython looks for a code file on the board to run. There are four options:code.txt,code.py,main.txt andmain.py. CircuitPython looks for those files, in that order, and then runs the first one it finds. Whilecode.py is the recommended name for your code file, it is important to know that the other options exist. If your program doesn't seem to be updating as you work, make sure you haven't created another code file that's being read instead of the one you're working on.