code: def _enable_pin(pin, direction):
      
      _write_value(pin, "{}/export".format(_path_prefix))
      _write_value(direction, "{0}/gpio{1}/direction".format(_path_prefix, pin))
docs: In order to enable a GPIO pin, the pin number must be written into
      /sys/class/gpio/export, and then the direction ("in" or "out" must be
      written to /sys/class/gpio/gpio<number>/direction
  
      :param pin: An integer corresponding to the GPIO number of the pin in RPi
        GPIO board numbering (not physical pin numbering)
  
      :param direction: "in" or "out"