11. Development¶

The main GitHub repository for the project can be found at:

https://github.com/RPi-Distro/python-gpiozero

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 DigitalOutputDevice. 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).

11.1. 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 git-core \
>   exuberant-ctags virtualenvwrapper python-virtualenv python3-virtualenv \
>   python-dev python3-dev
$ cd
$ mkvirtualenv -p /usr/bin/python3 python-gpiozero
$ workon python-gpiozero
(python-gpiozero) $ git clone https://github.com/RPi-Distro/python-gpiozero.git
(python-gpiozero) $ cd python-gpiozero
(python-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 largely experimental at this stage and not very useful):

(python-gpiozero) $ pip install rpi.gpio pigpio

If you are working on SPI devices you may also wish to install the spidev package to provide hardware SPI capabilities (again, GPIO Zero will work without this, but a big-banging software SPI implementation will be used instead):

(python-gpiozero) $ pip install spidev

To pull the latest changes from git into your clone and update your installation:

$ workon python-gpiozero
(python-gpiozero) $ cd ~/python-gpiozero
(python-gpiozero) $ git pull
(python-gpiozero) $ make develop

To remove your installation, destroy the sandbox and the clone:

(python-gpiozero) $ deactivate
$ rmvirtualenv python-gpiozero
$ rm -fr ~/python-gpiozero

11.2. 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 graphviz inkscape

Once these are installed, you can use the “doc” target to build the documentation:

$ workon python-gpiozero
(python-gpiozero) $ cd ~/python-gpiozero
(python-gpiozero) $ make doc

The HTML output is written to docs/_build/html while the PDF output goes to docs/_build/latex.

11.3. 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:

$ workon python-gpiozero
(python-gpiozero) $ cd ~/python-gpiozero
(python-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 GPIOZERO_TEST_PIN (defaults to 22) and GPIOZERO_TEST_INPUT_PIN (defaults to 27).

Warning

When wiring GPIOs together, ensure a load (like a 330Ω 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!).