GPIO Zero

or: Designing for Education is Hard

Vital Statistics

Name

Ben Nuttall

Occupation

The Pi'd Piper of Cambridge

Twitter

@ben_nuttall

GitHub

github.com/bennuttall

Vitalstatistix

Name

Dave Jones

Occupation

Making scary code, so you don't have to!

Twitter

@waveform80

GitHub

github.com/waveform80

So, what is it?

A library that makes physical computing easy

“Physical” computing?

LED blink

          import RPi.GPIO as GPIO
          from time import sleep

          GPIO.setmode(GPIO.BCM)
          GPIO.setwarnings(False)
          GPIO.setup(17, GPIO.OUT)

          while True:
              GPIO.output(17, GPIO.HIGH)
              sleep(1)
              GPIO.output(17, GPIO.LOW)
              sleep(1)
          

          from gpiozero import LED
          from time import sleep

          led = LED(17)

          while True:
              led.on()
              sleep(1)
              led.off()
              sleep(1)
          

          import RPi.GPIO as GPIO
          from time import sleep

          GPIO.setmode(GPIO.BCM)
          GIPO.setwarnings(False)
          GPIO.setup(18, GPIO.IN, GPIO.PUD_UP)

          GPIO.wait_for_edge(18, GPIO.FALLING)
          print("Don't push the button!")
          

          from gpiozero import Button
          from time import sleep

          button = Button(18)
          button.wait_for_press()
          print("Don't push the button!")
          

Why?

You see things; and you say "Why?" But I dream things that never were; and I say "Why not?"

— George Bernard Shaw, Back to Methuselah

Why not?

Because you're making it too easy!

— John Q. Public, The Internet

Lesson 1:

There's no such thing as “too easy”

Query a web-page

requests

urllib

socket

But that's work, we're talking about education. It's meant to be harder!

— John Q. Public, The Internet

          from gpiozero import LED
          from time import sleep

          led = LED(17)

          while True:
              led.on()
              sleep(1)
              led.off()
              sleep(1)
          

          from gpiozero import LED
          from time import sleep

          led = LED(17)
          led.blink()
          

          from gpiozero import LED
          from time import sleep
          from signal import pause

          led = LED(17)
          led.blink()
          pause()
          

Lesson 2:

“Easy” is a continuum

Why is Python great for teaching?

          do_this()
          do_that()
          if this:
              do_one_thing()
          else:
              do_another()
          

          def do_this():
              return that

          while True:
              that = do_this()
              if not that:
                  break
          

          class Animal(Eukaryote):
              def eat(self, food): # ...
              def excrete(self, where): # ...

          class Fungi(Eukaryote):
              def sit_around(self): # ...
              def release_spores(self, n): # ...
          

And GPIO Zero?

          from gpiozero import LED, Button

          led = LED(17)
          btn = Button(2)

          while True:
              if btn.is_pressed:
                  led.on()
              else:
                  led.off()
          

          from gpiozero import LED, Button
          from signal import pause

          led = LED(17)
          btn = Button(2)

          btn.when_pressed = led.on
          btn.when_released = led.off
          pause()
          

          from gpiozero import LED, Button
          from signal import pause

          led = LED(17)
          btn = Button(2)

          led.source = btn.values
          pause()
          

Lesson 3:

Making things easy is hard

Dive Dive Dive!

          class LED(DigitalOutputDevice):
              pass
          

          class DigitalOutputDevice(OutputDevice):
              def __init__(
                  self, pin=None, active_high=True,
                  initial_value=False): # ...
              def close(self): # ...
              def on(self): # ...
              def off(self): # ...
              def blink(
                  self, on_time=1, off_time=1, n=None,
                  background=True): # ...
          

          class OutputDevice(SourceMixin, GPIODevice):
              def __init__(
                  self, pin=None, active_high=True,
                  initial_value=False): # ...
              def on(self): # ...
              def off(self): # ...
              def toggle(self): # ...
              @property
              def value(self): # ...
              @property
              def active_high(self): # ...
          

          class GPIODevice(Device):
              def __init__(self, pin=None): # ...
              def close(self): # ...
              @property
              def closed(self): # ...
              @property
              def pin(self): # ...
              @property
              def value(self): # ...
          

          class Device(ValuesMixin, GPIOBase):
              @property
              def value(self): # ...
              @property
              def is_active(self): # ...
          

          class GPIOBase(GPIOMeta(nstr('GPIOBase'), (), {})):
              def __setattr__(self, name, value): # ...
              def __del__(self): # ...
              def close(self): # ...
              @property
              def closed(self): # ...
              def __enter__(self): # ...
              def __exit__(self, exc_type, exc_value, exc_tb): # ...
          

          class GPIOBase(GPIOMeta(nstr('GPIOBase'), (), {})):
              def __setattr__(self, name, value): # ...
              def __del__(self): # ...
              def close(self): # ...
              @property
              def closed(self): # ...
              def __enter__(self): # ...
              def __exit__(self, exc_type, exc_value, exc_tb): # ...
          

Meta-classes: why?!

Lesson 4:

Debugging is a hard skill

Challenge:

What went wrong…?

          from gpiozero import Button
          from signal import pause

          def button_was_pressed():
              print("Don't push the button!")

          b = Button(21)
          b.pressed = button_was_pressed
          pause()
          

          Traceback (most recent call last):
            File "dont_push.py", line 8, in 
            File "gpiozero/devices.py", line 158, in __setattr__
              self.__class__.__name__, name))
          AttributeError: 'Button' object has no attribute 'pressed'
          

More Horror!

          import inspect # OH NOES!
          import weakref
          from functools import wraps
          from threading import Event
          from collections import deque
          from time import time
          try:
              from statistics import median
          except ImportError:
              from .compat import median
          

          class EventsMixin(object):
              # ...

              @when_activated.setter
              def when_activated(self, value):
                  # That doesn't sound good ...
                  self._when_activated = self._wrap_callback(value)
          

              def _wrap_callback(self, fn):
                  if fn is None:
                      return None
                  elif inspect.isbuiltin(fn):
                      return fn
                  else:
                      try:
                          inspect.getcallargs(fn)
                          return fn
                      except TypeError:
                          inspect.getcallargs(fn, self)
                          @wraps(fn)
                          def wrapper():
                              return fn(self)
                          return wrapper
          

No boilerplate!

          from gpiozero import Button
          from signal import pause

          def button_was_pressed(btn): # <--- mandatory parameter
              print("Don't push the button!")

          b = Button(21)
          b.when_pressed = button_was_pressed
          pause()
          

          from gpiozero import Button
          from signal import pause

          def button_was_pressed(): # <--- not so mandatory parameter
              print("Don't push the button!")

          b = Button(21)
          b.when_pressed = button_was_pressed
          pause()
          

More WAT?

So that declarative thing …

          from gpiozero import LED, Button
          from signal import pause

          led = LED(17)
          btn = Button(2)

          led.source = btn.values
          pause()
          

          from gpiozero import LED, Button
          from gpiozero.tools import all_values
          from signal import pause

          led = LED(17)
          btn1 = Button(2)
          btn2 = Button(3)

          led.source = all_values(btn1.values, btn2.values)
          pause()
          

          from gpiozero import Energenie, Button
          from signal import pause

          lamp = Energenie(1)
          btn = Button(2)

          lamp.source = btn.values
          pause()
          

          from gpiozero import Robot, MCP3008
          from signal import pause

          robot = Robot(left=(17, 18), right=(3, 4))
          left_pot = MCP3008(channel=0)
          right_pot = MCP3008(channel=1)

          # TANK!!!
          robot.source = zip(left_pot.values, right_pot.values)
          pause()
          

          from gpiozero import Energenie, MCP3008
          from gpiozero.tools import booleanized
          from signal import pause

          heater = Energenie(1)
          thermometer = MCP3008(channel=0)

          heater.source = booleanized(thermometer.values, 0.0, 0.5)
          pause()
          

          from gpiozero import Energenie, MCP3008
          from gpiozero.tools import booleanized
          from signal import pause

          heater = Energenie(1)
          thermometer = MCP3008(channel=0)

          heater.source = booleanized(thermometer.values, 0.0, 0.5,
              hysteresis=0.1)
          pause()
          

          from travispy import TravisPy
          from gpiozero import LED
          from gpiozero.tools import negated
          from time import sleep
          from signal import pause

          def status(repo, delay=3600):
              t = TravisPy()
              r = t.repo(repo)
              while True:
                  yield r.last_build_state == 'passed'
                  sleep(delay) # don't hit Travis constantly

          tl = TrafficLights(21, 20, 16)
          tl.red.source = negated(tl.green.values)
          tl.green.source = status('RPi-Distro/python-gpiozero')
          pause()
          

Pin implementations

Remote pins?!

          $ export GPIOZERO_PIN_FACTORY=PiGPIOPin
          $ export PIGPIO_ADDR=192.168.1.5
          $ python
          

Runs on

Cool toys!

Timeline

Community growth

Issue driven development

Future Development

• Support more devices
• Move default pins to PiGPIO
• Remote SPI and I2C support
• Promote zero boilerplate philosophy in other projects

GPIO Zero

Documents

gpiozero.readthedocs.io

GitHub

github.com/RPi-Distro/python-gpiozero

Join us!

at the sprints tomorrow

Thank You

Questions?