9. Frequently Asked Questions¶
9.1. How do I keep my script running?¶
The following script looks like it should turn an
from gpiozero import LED led = LED(17) led.on()
And it does, if you’re using the Python or IPython shell, or the IDLE, Thonny or Mu editors. However, if you saved this script as a Python file and ran it, it would flash on briefly, then the script would end and it would turn off.
The following file includes an intentional
pause() to keep the
from gpiozero import LED from signal import pause led = LED(17) led.on() pause()
Now the script will stay running, leaving the LED on, until it is terminated manually (e.g. by pressing Ctrl+C). Similarly, when setting up callbacks on button presses or other input devices, the script needs to be running for the events to be detected:
from gpiozero import Button from signal import pause def hello(): print("Hello") button = Button(2) button.when_pressed = hello pause()
9.2. What’s the difference between when_pressed, is_pressed and wait_for_press?¶
gpiozero provides a range of different approaches to reading input devices. Sometimes you want to ask if a button’s pressed, sometimes you want to do something until it’s pressed, and sometimes you want something to happen when it’s been pressed, regardless of what else is going on.
In a simple example where the button is the only device in play, all of the options would be equally effective. But as soon as you introduce an extra element, like another GPIO device, you might need to choose the right approach depending on your use case.
is_pressedis an attribute which reveals whether the button is currently pressed by returning
while True: if btn.is_pressed: print("Pressed") else: print("Not pressed")
while True: print("Released. Waiting for press..") btn.wait_for_press() print("Pressed. Waiting for release...") btn.wait_for_release()
when_pressedis an attribute which assigns a callback function to the event of the button being pressed. Every time the button is pressed, the callback function is executed in a separate thread. Also see
def pressed(): print("Pressed") def released(): print("Released") btn.when_pressed = pressed btn.when_released = released
This pattern of options is common among many devices. All input devices and internal devices have
wait_for_inactive, and many provide aliases (such as “pressed” for
Also see a more advanced approach in the Source/Values page.
9.3. My event handler isn’t being called¶
When assigning event handlers, don’t call the function you’re assigning. For example:
from gpiozero import Button def pushed(): print("Don't push the button!") b = Button(17) b.when_pressed = pushed()
In the case above, when assigning to
when_pressed, the thing
that is assigned is the result of calling the
pushed function. Because
pushed doesn’t explicitly return anything, the result is
Hence this is equivalent to doing:
b.when_pressed = None
This doesn’t raise an error because it’s perfectly valid: it’s what you assign when you don’t want the event handler to do anything. Instead, you want to do the following:
b.when_pressed = pushed
This will assign the function to the event handler without calling it. This
is the crucial difference between
my_function (a reference to a function)
my_function() (the result of calling a function).
Note that as of v1.5, setting a callback to
None when it was
None will raise a
with the intention of alerting users when callbacks are set to
accidentally. However, if this is intentional, the warning can be
suppressed. See the
warnings module for reference.
9.4. Why do I get PinFactoryFallback warnings when I import gpiozero?¶
You are most likely working in a virtual Python environment and have forgotten
to install a pin driver library like
RPi.GPIO. GPIO Zero relies upon lower
level pin drivers to handle interfacing to the GPIO pins on the Raspberry Pi,
so you can eliminate the warning simply by installing GPIO Zero’s first
$ pip install rpi.gpio
When GPIO Zero is imported it attempts to find a pin driver by importing them
in a preferred order (detailed in API - Pins). If it fails to load its
first preference (
RPi.GPIO) it notifies you with a warning, then falls back
to trying its second preference and so on. Eventually it will fall back all the
way to the
native implementation. This is a pure Python implementation
built into GPIO Zero itself. While this will work for most things it’s almost
certainly not what you want (it doesn’t support PWM, and it’s quite slow at
If you want to use a pin driver other than the default, and you want to suppress the warnings you’ve got a couple of options:
Explicitly specify what pin driver you want via the
GPIOZERO_PIN_FACTORYenvironment variable. For example:
$ GPIOZERO_PIN_FACTORY=pigpio python3
In this case no warning is issued because there’s no fallback; either the specified factory loads or it fails in which case an
ImportErrorwill be raised.
Suppress the warnings and let the fallback mechanism work:
>>> import warnings >>> warnings.simplefilter('ignore') >>> import gpiozero
Refer to the
warningsmodule documentation for more refined ways to filter out specific warning classes.
9.5. How can I tell what version of gpiozero I have installed?¶
The gpiozero library relies on the setuptools package for installation
services. You can use the setuptools
pkg_resources API to query which
version of gpiozero is available in your Python environment like so:
>>> from pkg_resources import require >>> require('gpiozero') [gpiozero 1.6.0 (/usr/lib/python3/dist-packages)] >>> require('gpiozero').version '1.6.0'
If you have multiple versions installed (e.g. from pip and
apt) they will not show up in the list returned by the
pkg_resources.require() method. However, the first entry in the list will
be the version that
import gpiozero will import.
If you receive the error “No module named pkg_resources”, you need to install pip. This can be done with the following command in Raspberry Pi OS:
$ sudo apt install python3-pip
Alternatively, install pip with get-pip.
9.6. Why do I get “command not found” when running pinout?¶
The gpiozero library is available as a Debian package for Python 2 and Python 3, but the pinout tool cannot be made available by both packages, so it’s only included with the Python 3 version of the package. To make sure the pinout tool is available, the “python3-gpiozero” package must be installed:
$ sudo apt install python3-gpiozero
Alternatively, installing gpiozero using pip will install the command line tool, regardless of Python version:
$ sudo pip3 install gpiozero
$ sudo pip install gpiozero
9.7. The pinout command line tool incorrectly identifies my Raspberry Pi model¶
If your Raspberry Pi model is new, it’s possible it wasn’t known about at the time of the gpiozero release you are using. Ensure you have the latest version installed (remember, the pinout tool usually comes from the Python 3 version of the package as noted in the previous FAQ).
If the Pi model you are using isn’t known to gpiozero, it may have been added
since the last release. You can check the GitHub issues to see if it’s been
reported before, or check the commits on GitHub since the last release to
see if it’s been added. The model determination can be found in
9.8. What’s the gpiozero equivalent of GPIO.cleanup()?¶
Many people ask how to do the equivalent of the
cleanup function from
RPi.GPIO. In gpiozero, at the end of your script, cleanup is run
automatically, restoring your GPIO pins to the state they were found.
To explicitly close a connection to a pin, you can manually call the
close() method on a device object:
>>> led = LED(2) >>> led.on() >>> led <gpiozero.LED object on pin GPIO2, active_high=True, is_active=True> >>> led.close() >>> led <gpiozero.LED object closed>
This means that you can reuse the pin for another device, and that despite
turning the LED on (and hence, the pin high), after calling
close() it is restored to its previous state (LED off, pin low).
Read more about Migrating from RPi.GPIO.
9.10. Why do I get “ImportError: cannot import name” when trying to import from gpiozero?¶
It’s common to see people name their first gpiozero script
Unfortunately, this will cause your script to try to import itself, rather than
the gpiozero library from the libraries path. You’ll see an error like this:
Traceback (most recent call last): File "gpiozero.py", line 1, in <module> from gpiozero import LED File "/home/pi/gpiozero.py", line 1, in <module> from gpiozero import LED ImportError: cannot import name 'LED'
Simply rename your script to something else, and run it again. Be sure not to
name any of your scripts the same name as a Python module you may be importing,
9.11. Why do I get an AttributeError trying to set attributes on a device object?¶
If you try to add an attribute to a gpiozero device object after its initialization, you’ll find you can’t:
>>> from gpiozero import Button >>> btn = Button(2) >>> btn.label = 'alarm' Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python3/dist-packages/gpiozero/devices.py", line 118, in __setattr__ self.__class__.__name__, name)) AttributeError: 'Button' object has no attribute 'label'
This is in order to prevent users accidentally setting new attributes by mistake. Because gpiozero provides functionality through setting attributes via properties, such as callbacks on buttons (and often there is no immediate feedback when setting a property), this could lead to bugs very difficult to find. Consider the following example:
from gpiozero import Button def hello(): print("hello") btn = Button(2) btn.pressed = hello
This is perfectly valid Python code, and no errors would occur, but the program
would not behave as expected: pressing the button would do nothing, because the
property for setting a callback is
without gpiozero preventing this non-existent attribute from being set, the
user would likely struggle to see the mistake.
If you really want to set a new attribute on a device object, you need to create it in the class before initializing your object:
>>> from gpiozero import Button >>> Button.label = '' >>> btn = Button(2) >>> btn.label = 'alarm' >>> def press(btn): ...: print(btn.label, "was pressed") >>> btn.when_pressed = press
9.12. Why is it called GPIO Zero? Does it only work on Pi Zero?¶
gpiozero works on all Raspberry Pi models, not just the Pi Zero.
These libraries aim to remove barrier to entry and provide a smooth learning curve for beginners by making it easy to get started and easy to build up to more advanced projects.