code: def start(self, pin, dutycycle, frequency_hz=2000):
          
          if dutycycle < 0.0 or dutycycle > 100.0:
              raise ValueError('Invalid duty cycle value, must be between 0.0 to 100.0 (inclusive).')
          # Make pin an output.
          self.rpi_gpio.setup(pin, self.rpi_gpio.OUT)
          # Create PWM instance and save a reference for later access.
          self.pwm[pin] = self.rpi_gpio.PWM(pin, frequency_hz)
          # Start the PWM at the specified duty cycle.
          self.pwm[pin].start(dutycycle)
docs: Enable PWM output on specified pin.  Set to intiial percent duty cycle
          value (0.0 to 100.0) and frequency (in Hz).