mirror of
https://github.com/KevinMidboe/python-gpiozero.git
synced 2025-10-29 17:50:37 +00:00
106 lines
2.7 KiB
ReStructuredText
106 lines
2.7 KiB
ReStructuredText
=====
|
|
Notes
|
|
=====
|
|
|
|
.. currentmodule:: gpiozero
|
|
|
|
|
|
.. _keep-your-script-running:
|
|
|
|
Keep your script running
|
|
========================
|
|
|
|
The following script looks like it should turn an LED on::
|
|
|
|
from gpiozero import LED
|
|
|
|
led = LED(17)
|
|
led.on()
|
|
|
|
And it does, if you're using the Python (or IPython or IDLE) shell. 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 :func:`~signal.pause` to keep the
|
|
script alive::
|
|
|
|
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()
|
|
|
|
|
|
Importing from GPIO Zero
|
|
========================
|
|
|
|
In Python, libraries and functions used in a script must be imported by name
|
|
at the top of the file, with the exception of the functions built into Python
|
|
by default.
|
|
|
|
For example, to use the :class:`Button` interface from GPIO Zero, it
|
|
should be explicitly imported::
|
|
|
|
from gpiozero import Button
|
|
|
|
Now :class:`~gpiozero.Button` is available directly in your script::
|
|
|
|
button = Button(2)
|
|
|
|
Alternatively, the whole GPIO Zero library can be imported::
|
|
|
|
import gpiozero
|
|
|
|
In this case, all references to items within GPIO Zero must be prefixed::
|
|
|
|
button = gpiozero.Button(2)
|
|
|
|
|
|
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:
|
|
|
|
.. code-block:: pycon
|
|
|
|
>>> from pkg_resources import require
|
|
>>> require('gpiozero')
|
|
[gpiozero 1.3.2 (/usr/lib/python3/dist-packages)]
|
|
>>> require('gpiozero')[0].version
|
|
'1.3.2'
|
|
|
|
If you have multiple versions installed (e.g. from ``pip`` and ``apt``) they
|
|
will not show up in the list returned by the ``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
|
|
the ``pip`` utility. This can be done with the following command in Raspbian:
|
|
|
|
.. code-block:: console
|
|
|
|
sudo apt install python-pip
|
|
|
|
Alternatively, install pip with `get-pip`_.
|
|
|
|
|
|
.. _get_pip: https://pip.pypa.io/en/stable/installing/
|