python-gpiozero/docs/notes.rst

=====
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(2)
    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(2)
    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)