How to use the gphoto2.gp_widget_get_value function in gphoto2

camera = gp.Camera()
        context = gp.gp_context_new()
        camera.init(context)
        config = camera.get_config(context)
        # find the date/time setting config item and get it
        # name varies with camera driver
        #   Canon EOS350d - 'datetime'
        #   PTP - 'd034'
        for name, fmt in (('datetime', '%Y-%m-%d %H:%M:%S'),
                          ('d034',     None)):
            OK, datetime_config = gp.gp_widget_get_child_by_name(config, name)
            if OK >= gp.GP_OK:
                widget_type = gp.check_result(gp.gp_widget_get_type(datetime_config))
                if widget_type == gp.GP_WIDGET_DATE:
                    raw_value = gp.check_result(
                        gp.gp_widget_get_value(datetime_config))
                    camera_time = datetime.fromtimestamp(raw_value)
                else:
                    raw_value = gp.check_result(
                        gp.gp_widget_get_value(datetime_config))
                    if fmt:
                        camera_time = datetime.strptime(raw_value, fmt)
                    else:
                        camera_time = datetime.utcfromtimestamp(float(raw_value))
                break
        imgfmtselected, imgfmtoptions   = readRange (camera, context, 'imgsettings', 'imageformat')
        wbselected, wboptions           = readRange (camera, context, 'imgsettings', 'whitebalance')
        isoselected, isooptions         = readRange (camera, context, 'imgsettings', 'iso')
        apselected, apoptions           = readRange (camera, context, 'capturesettings', 'aperture')
        shutselected, shutoptions       = readRange (camera, context, 'capturesettings', 'shutterspeed')
        expselected, expoptions         = readRange (camera, context, 'capturesettings', 'exposurecompensation')

def main():
    logging.basicConfig(
        format='%(levelname)s: %(name)s: %(message)s', level=logging.WARNING)
    callback_obj = gp.check_result(gp.use_python_logging())
    camera = gp.check_result(gp.gp_camera_new())
    gp.check_result(gp.gp_camera_init(camera))
    # required configuration will depend on camera type!
    print('Checking camera config')
    # get configuration tree
    config = gp.check_result(gp.gp_camera_get_config(camera))
    # find the image format config item
    # camera dependent - 'imageformat' is 'imagequality' on some
    OK, image_format = gp.gp_widget_get_child_by_name(config, 'imageformat')
    if OK >= gp.GP_OK:
        # get current setting
        value = gp.check_result(gp.gp_widget_get_value(image_format))
        # make sure it's not raw
        if 'raw' in value.lower():
            print('Cannot preview raw images')
            return 1
    # find the capture size class config item
    # need to set this on my Canon 350d to get preview to work at all
    OK, capture_size_class = gp.gp_widget_get_child_by_name(
        config, 'capturesizeclass')
    if OK >= gp.GP_OK:
        # set value
        value = gp.check_result(gp.gp_widget_get_choice(capture_size_class, 2))
        gp.check_result(gp.gp_widget_set_value(capture_size_class, value))
        # set config
        gp.check_result(gp.gp_camera_set_config(camera, config))
    # capture preview image (not saved to camera memory card)
    print('Capturing preview image')

def getPreviewImage(camera, context, config):
    """ Straight out of Jim's examples """
    OK, image_format = gp.gp_widget_get_child_by_name(config, 'imageformat')
    if OK >= gp.GP_OK:
        # get current setting
        value = gp.check_result(gp.gp_widget_get_value(image_format))
        # make sure it's not raw
        if 'raw' in value.lower():
            app.logger.debug('Cannot preview raw images')
            return 1
    # find the capture size class config item
    # need to set this on my Canon 350d to get preview to work at all
    OK, capture_size_class = gp.gp_widget_get_child_by_name(
        config, 'capturesizeclass')
    if OK >= gp.GP_OK:
        # set value
        value = gp.check_result(gp.gp_widget_get_choice(capture_size_class, 2))
        gp.check_result(gp.gp_widget_set_value(capture_size_class, value))
        # set config
        gp.check_result(gp.gp_camera_set_config(camera, config))
    # capture preview image (not saved to camera memory card)
    app.logger.debug('Capturing preview image')

def readValue ( camera, attribute ):
    """ Reads a simple attribute in the camera and returns the value """
    try:
        object = gp.check_result(gp.gp_widget_get_child_by_name(camera, attribute))
        value = gp.check_result(gp.gp_widget_get_value(object))
    except:
        value = ''
    return value

def readValue ( camera, attribute ):
    """ Reads a simple attribute in the camera and returns the value """
    try:
        object = gp.check_result(gp.gp_widget_get_child_by_name(camera, attribute))
        value = gp.check_result(gp.gp_widget_get_value(object))
    except:
        value = ''
    return value

def getPreviewImage(camera, context, config):
    """ Straight out of Jim's examples """
    OK, image_format = gp.gp_widget_get_child_by_name(config, 'imageformat')
    if OK >= gp.GP_OK:
        # get current setting
        value = gp.check_result(gp.gp_widget_get_value(image_format))
        # make sure it's not raw
        if 'raw' in value.lower():
            app.logger.debug('Cannot preview raw images')
            return 1
    # find the capture size class config item
    # need to set this on my Canon 350d to get preview to work at all
    OK, capture_size_class = gp.gp_widget_get_child_by_name(
        config, 'capturesizeclass')
    if OK >= gp.GP_OK:
        # set value
        value = gp.check_result(gp.gp_widget_get_choice(capture_size_class, 2))
        gp.check_result(gp.gp_widget_set_value(capture_size_class, value))
        # set config
        gp.check_result(gp.gp_camera_set_config(camera, config))
    # capture preview image (not saved to camera memory card)
    app.logger.debug('Capturing preview image')