The main GitHub repository for the project can be found at:
For anybody wishing to hack on the project, we recommend starting off by
getting to grips with some simple device classes. Pick something like
LED and follow its heritage backward to
Follow that back to
OutputDevice and you should have a good
understanding of simple output devices along with a grasp of how GPIO Zero
relies fairly heavily upon inheritance to refine the functionality of devices.
The same can be done for input devices, and eventually more complex devices
(composites and SPI based).
13.1. Development installation
If you wish to develop GPIO Zero itself, we recommend obtaining the source by cloning the GitHub repository and then use the “develop” target of the Makefile which will install the package as a link to the cloned repository allowing in-place development (it also builds a tags file for use with vim/emacs with Exuberant’s ctags utility). The following example demonstrates this method within a virtual Python environment:
$ sudo apt install lsb-release build-essential git exuberant-ctags \ virtualenvwrapper python-virtualenv python3-virtualenv \ python-dev python3-dev
virtualenvwrapper you’ll need to restart your shell before
commands like mkvirtualenv will operate correctly. Once you’ve
restarted your shell, continue:
$ cd $ mkvirtualenv -p /usr/bin/python3 gpiozero $ workon gpiozero (gpiozero) $ git clone https://github.com/gpiozero/gpiozero.git (gpiozero) $ cd gpiozero (gpiozero) $ make develop
You will likely wish to install one or more pin implementations within the virtual environment (if you don’t, GPIO Zero will use the “native” pin implementation which is usable at this stage, but doesn’t support facilities like PWM):
(gpiozero) $ pip install rpi.gpio pigpio
If you are working on SPI devices you may also wish to install the
package to provide hardware SPI capabilities (again, GPIO Zero will work
without this, but a big-banging software SPI implementation will be used
instead which limits bandwidth):
(gpiozero) $ pip install spidev
To pull the latest changes from git into your clone and update your installation:
$ workon gpiozero (gpiozero) $ cd ~/gpiozero (gpiozero) $ git pull (gpiozero) $ make develop
To remove your installation, destroy the sandbox and the clone:
(gpiozero) $ deactivate $ rmvirtualenv gpiozero $ rm -rf ~/gpiozero
13.2. Building the docs
If you wish to build the docs, you’ll need a few more dependencies. Inkscape is used for conversion of SVGs to other formats, Graphviz is used for rendering certain charts, and TeX Live is required for building PDF output. The following command should install all required dependencies:
$ sudo apt install texlive-latex-recommended texlive-latex-extra \ texlive-fonts-recommended texlive-xetex graphviz inkscape \ python3-sphinx python3-sphinx-rtd-theme latexmk xindy
Once these are installed, you can use the “doc” target to build the documentation:
$ workon gpiozero (gpiozero) $ cd ~/gpiozero (gpiozero) $ make doc
The HTML output is written to
build/html while the PDF output
13.3. Test suite
If you wish to run the GPIO Zero test suite, follow the instructions in Development installation above and then make the “test” target within the sandbox. You’ll also need to install some pip packages:
$ workon gpiozero (gpiozero) $ pip install coverage mock pytest (gpiozero) $ cd ~/gpiozero (gpiozero) $ make test
The test suite expects pins 22 and 27 (by default) to be wired together in
order to run the “real” pin tests. The pins used by the test suite can be
overridden with the environment variables
to 22) and
GPIOZERO_TEST_INPUT_PIN (defaults to 27).
When wiring GPIOs together, ensure a load (like a 1KΩ resistor) is placed between them. Failure to do so may lead to blown GPIO pins (your humble author has a fried GPIO27 as a result of such laziness, although it did take many runs of the test suite before this occurred!).
The test suite is also setup for usage with the tox utility, in which case it will attempt to execute the test suite with all supported versions of Python. If you are developing under Ubuntu you may wish to look into the Dead Snakes PPA in order to install old/new versions of Python; the tox setup should work with the version of tox shipped with Ubuntu Xenial, but more features (like parallel test execution) are available with later versions.
On the subject of parallel test execution, this is also supported in the tox setup, including the “real” pin tests (a file-system level lock is used to ensure different interpreters don’t try to access the physical pins simultaneously).
For example, to execute the test suite under tox, skipping interpreter versions which are not installed:
$ tox -s
To execute the test suite under all installed interpreter versions in parallel, using as many parallel tasks as there are CPUs, then displaying a combined report of coverage from all environments:
$ tox -p auto -s $ coverage combine --rcfile coverage.cfg $ coverage report --rcfile coverage.cfg
13.4. Mock pins
The test suite largely depends on the existence of the mock pin factory
MockFactory, which is also useful for manual
testing, for example in the Python shell or another REPL. See the section on
Mock pins in the API - Pins chapter for more information.