I want to set a callback function to run when an event occurs in a GPIO. I'm designing a class and I want to have the callback method inside it too. Here's an excerpt of the code:

import RPi.GPIO as gpio

class WheelEncoder:
  'Encapsulates the attributes and methods to use a wheel encoder sensor'

  inputPin = 0
  ticks = 0

  def __init__(self, inputPin):
    self.inputPin = inputPin

    gpio.setup(self.inputPin, gpio.IN, pull_up_down=gpio.PUD_UP)
    gpio.add_event_detect(self.inputPin, gpio.RISING, event_callback)

  def getTicks(self):
    return self.ticks

  def resetTicks(self):
    self.ticks = 0

  def event_callback(channel):
    self.ticks += 1

And here is the output of calling it (from another file):

Traceback (most recent call last):
  File "test-WheelEncoder.py", line 5, in <module>
    sensor = WheelEncoder(3, 10, 3)
  File "/home/pi/codes/sensors/WheelEncoder.py", line 20, in __init__
    gpio.add_event_detect(self.inputPin, gpio.RISING, event_callback)
NameError: global name 'event_callback' is not defined

Im not sure what it could be.


1 Answer 1


Just found the answer. I changed the call to add_event_detect to be

gpio.add_event_detect(self.inputPin, gpio.RISING, self.event_callback)

and changed the signature of event_callback to be

event_callback(self, channel):

The complete code can be seen in my own repository: https://github.com/luizfzs/python-pi-sensor-modules/blob/master/WheelEncoder.py#L28

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