backlight control doesn't work

Thanks for this library- I'm finding it easy to use!

I'm just playing with my new toy (Pi Pico) + pcf8574 i2c module, using the latest stable CircuitPython.

I tried to turn off/on the back light but got _BACKLIGHT_VALUES undefined erro in i2c_pcf8574_interface.py.

I modified it to:

    @backlight.setter
    def backlight(self, value):
        self._backlight_pin_state = I2CPCF8574Interface._BACKLIGHT_VALUES[value]
        self._i2c_write(self._backlight_pin_state)

but now get:

  File "/lib/lcd/lcd.py", line 158, in set_backlight
  File "/lib/lcd/i2c_pcf8574_interface.py", line 71, in backlight
  File "/lib/lcd/i2c_pcf8574_interface.py", line 96, in _i2c_write
RuntimeError: Function requires lock

My code:

lcd.set_backlight(False)

I'm new to i2c via CircuitPython, so not sure what to try next.

dhalbert / CircuitPython_LCD

backlight control doesn't work #7