gpiocrust

A concise, pythonic wrapper around the Raspberry Pi’s RPi.GPIO library. An encrusting, if you will.

With (almost silent) fallback to mock objects, you can prototype pin I/O locally on your favorite computer, even when your Pi is on the other side of town (see Mock API for more details).

gpiocrust is fully compatible with Python 2 and Python 3.

In a nutshell

Download from PyPI with easy_install or pip.

pip install gpiocrust

In a .py file, import the library and start setting pin values. It's easy! Here's a bare-bones example that will turn on GPIO pin 15:

from gpiocrust import Header, OutputPin

with Header() as header:
  pin = OutputPin(15, value=0)
  pin.value = 1

API

gpiocrust provides four classes to help give GPIO pin manipulation a more object-oriented feel. They are:

• Header
• OutputPin
• PWMOutputPin
• InputPin

Header

The Header class just wraps the GPIO setup and teardown methods. Most importantly, it ensures that GPIO.cleanup() is called. For example:

from gpiocrust import Header

with Header() as header:
  # Application logic goes here
  pass

# All cleaned up now.

OutputPin

The OutputPin class controls a single GPIO pin for output. Set its value to True (1) or False (0). That’s all there is to it!

from gpiocrust import Header, OutputPin

with Header() as header:
  shiny_led = OutputPin(11)
  shiny_led.value = True
  ...

value defaults to False, but can be set with a keyword argument.

shiny_led = OutputPin(11, value=True)

PWMOutputPin

The PWMOutputPin class controls a single GPIO pin for output, but allows for variable values via software pulse width modulation.

from gpiocrust import Header, PWMOutputPin

with Header() as header:
  soft_led = PWMOutputPin(11)
  soft_led.value = 0.25
  ...

You can set the frequency (Hz) via the frequency property. For example:

from gpiocrust import Header, PWMOutputPin

with Header() as header:
  soft_led = PWMOutputPin(11, frequency=100)
  soft_led.frequency = 50

NOTE: the RPi.GPIO implementation uses duty cycle values from 0 to 100. To be consistent with OutputPin, PWMOutputPin uses decimal values 0.0 to 1.0.

For a good overview of how to use the RPi.GPIO implementation, see this video.

InputPin

The InputPin class controls a single GPIO pin for input. You can watch for edge events using a callback argument or via the @change decorator. For now, InputPin only supports watching GPIO.BOTH (rising and falling) events.

from gpiocrust import Header, InputPin

def alert_president(value):
  pass

with Header() as header:
  the_red_button = InputPin(11, callback=alert_president)

It’s even cleaner with the @change decorator.

from gpiocrust import Header, InputPin

with Header() as header:
  the_red_button = InputPin(11, value=0)

  @the_red_button.change
  def alert_president(value):
    pass

Mock API

Mock classes are included that mimick the native GPIO functionality. The library falls back to mock objects when the RPi.GPIO package cannot be loaded. This allows one to code the general I/O flow of an application in development environments where running code on a physical Raspberry Pi is inconvenient or impossible (i.e, the computer you're reading this on).

Fallback is automatic, so your import statements will look just as before.

OutputPin example

import time
from gpiocrust import Header, OutputPin, PWMOutputPin

with Header() as header:
  pin11 = OutputPin(11)
  pin15 = PWMOutputPin(15, frequency=100, value=0)

  try:
    while 1:
      # Going up
      pin11.value = True

      for i in range(100):
        pin15.value = i / 100.0
        time.sleep(0.01)

      time.sleep(0.5)

      # Going down
      pin11.value = False

      for i in range(100):
        pin15.value = (100 - i) / 100.0
        time.sleep(0.01)

      time.sleep(0.5)
  except KeyboardInterrupt:
    pass