mirror of
https://github.com/KevinMidboe/python-gpiozero.git
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Split Notes into FAQ and Recipes
Notes was always a bit of a "vague" section and half of it felt like FAQs. Hopefully this is a little more consistent
This commit is contained in:
Dave Jones
74
docs/faq.rst
74
docs/faq.rst
@@ -84,3 +84,77 @@ suppress the warnings you've got a couple of options:
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Refer to the :mod:`warnings` module documentation for more refined ways to
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filter out specific warning classes.
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How can I tell what version of gpiozero I have installed?
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=========================================================
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The gpiozero library relies on the setuptools package for installation
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services. You can use the setuptools ``pkg_resources`` API to query which
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version of gpiozero is available in your Python environment like so:
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.. code-block:: pycon
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>>> from pkg_resources import require
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>>> require('gpiozero')
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[gpiozero 1.3.2 (/usr/lib/python3/dist-packages)]
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>>> require('gpiozero')[0].version
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'1.3.2'
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If you have multiple versions installed (e.g. from ``pip`` and ``apt``) they
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will not show up in the list returned by the ``require`` method. However, the
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first entry in the list will be the version that ``import gpiozero`` will
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import.
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If you receive the error "No module named pkg_resources", you need to install
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the ``pip`` utility. This can be done with the following command in Raspbian:
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.. code-block:: console
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$ sudo apt install python-pip
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Alternatively, install pip with `get-pip`_.
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.. _get-pip: https://pip.pypa.io/en/stable/installing/
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.. _keep-your-script-running:
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How do I keep my script running?
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================================
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The following script looks like it should turn an LED on::
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from gpiozero import LED
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led = LED(17)
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led.on()
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And it does, if you're using the Python (or IPython or IDLE) shell. However,
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if you saved this script as a Python file and ran it, it would flash on
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briefly, then the script would end and it would turn off.
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The following file includes an intentional :func:`~signal.pause` to keep the
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script alive::
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from gpiozero import LED
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from signal import pause
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led = LED(17)
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led.on()
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pause()
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Now the script will stay running, leaving the LED on, until it is terminated
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manually (e.g. by pressing Ctrl+C). Similarly, when setting up callbacks on
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button presses or other input devices, the script needs to be running for the
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events to be detected::
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from gpiozero import Button
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from signal import pause
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def hello():
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print("Hello")
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button = Button(2)
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button.when_pressed = hello
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pause()
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@@ -8,7 +8,6 @@ Table of Contents
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:numbered:
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recipes
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notes
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installing
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api_input
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api_output
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105
docs/notes.rst
105
docs/notes.rst
@@ -1,105 +0,0 @@
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=====
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Notes
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=====
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.. currentmodule:: gpiozero
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.. _keep-your-script-running:
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Keep your script running
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========================
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The following script looks like it should turn an LED on::
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from gpiozero import LED
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led = LED(17)
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led.on()
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And it does, if you're using the Python (or IPython or IDLE) shell. However,
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if you saved this script as a Python file and ran it, it would flash on
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briefly, then the script would end and it would turn off.
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The following file includes an intentional :func:`~signal.pause` to keep the
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script alive::
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from gpiozero import LED
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from signal import pause
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led = LED(17)
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led.on()
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pause()
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Now the script will stay running, leaving the LED on, until it is terminated
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manually (e.g. by pressing Ctrl+C). Similarly, when setting up callbacks on
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button presses or other input devices, the script needs to be running for the
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events to be detected::
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from gpiozero import Button
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from signal import pause
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def hello():
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print("Hello")
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button = Button(2)
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button.when_pressed = hello
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pause()
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Importing from GPIO Zero
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========================
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In Python, libraries and functions used in a script must be imported by name
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at the top of the file, with the exception of the functions built into Python
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by default.
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For example, to use the :class:`Button` interface from GPIO Zero, it
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should be explicitly imported::
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from gpiozero import Button
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Now :class:`~gpiozero.Button` is available directly in your script::
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button = Button(2)
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Alternatively, the whole GPIO Zero library can be imported::
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import gpiozero
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In this case, all references to items within GPIO Zero must be prefixed::
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button = gpiozero.Button(2)
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How can I tell what version of gpiozero I have installed?
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=========================================================
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The gpiozero library relies on the setuptools package for installation
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services. You can use the setuptools ``pkg_resources`` API to query which
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version of gpiozero is available in your Python environment like so:
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.. code-block:: pycon
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>>> from pkg_resources import require
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>>> require('gpiozero')
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[gpiozero 1.3.2 (/usr/lib/python3/dist-packages)]
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>>> require('gpiozero')[0].version
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'1.3.2'
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If you have multiple versions installed (e.g. from ``pip`` and ``apt``) they
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will not show up in the list returned by the ``require`` method. However, the
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first entry in the list will be the version that ``import gpiozero`` will
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import.
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If you receive the error "No module named pkg_resources", you need to install
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the ``pip`` utility. This can be done with the following command in Raspbian:
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.. code-block:: console
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sudo apt install python-pip
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Alternatively, install pip with `get-pip`_.
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.. _get-pip: https://pip.pypa.io/en/stable/installing/
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@@ -24,6 +24,31 @@ example, if an LED was attached to "GPIO17" you would specify the pin number as
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17 rather than 11:
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.. image:: images/pin_layout.*
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:align: center
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Importing GPIO Zero
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===================
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In Python, libraries and functions used in a script must be imported by name
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at the top of the file, with the exception of the functions built into Python
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by default.
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For example, to use the :class:`Button` interface from GPIO Zero, it
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should be explicitly imported::
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from gpiozero import Button
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Now :class:`~gpiozero.Button` is available directly in your script::
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button = Button(2)
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Alternatively, the whole GPIO Zero library can be imported::
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import gpiozero
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In this case, all references to items within GPIO Zero must be prefixed::
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button = gpiozero.Button(2)
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LED
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===
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