Rotary encoder on Raspberry Pi

rotary.py

import RPi.GPIO as GPIO
import threading

GPIO.setmode(GPIO.BCM)

class RotaryEncoder:
    def __init__(self, pin_a, pin_b):
        self.pin_a = pin_a
        self.pin_b = pin_b

        self.state_a = None
        self.state_b = None
        self.count = 0
        self.lock = threading.Lock()

        GPIO.setup(pin_a, GPIO.IN, pull_up_down=GPIO.PUD_UP)
        GPIO.setup(pin_b, GPIO.IN, pull_up_down=GPIO.PUD_UP)

        def callback(channel):
            switch_a = GPIO.input(self.pin_a)
            switch_b = GPIO.input(self.pin_b)
                else:
            if (switch_a, switch_b) == (self.state_a, self.state_b):
                # nothing changed
                return

            # print(switch_a, switch_b)

            if switch_a and switch_b:
                # rotation is complete, which direction?
                self.lock.acquire()
                if channel == self.pin_a:
                    self.count += 1
                else:
                    self.count -= 1
                self.lock.release()
                self.update()

        GPIO.add_event_detect(self.pin_a, GPIO.BOTH, callback=callback)
        GPIO.add_event_detect(self.pin_b, GPIO.BOTH, callback=callback)

    def update(self):
        print("count", self.count)

r = RotaryEncoder(17, 27)

if __name__ == "__main__":
    try:
        import time
        while True:
            time.sleep(1)
    finally:
        GPIO.cleanup()