def validate(self):
        """ Checks whether the backbone string is correct.
        """
        backbone = self.backbone.split('_')[0]

        if backbone not in MobileNetBackbone.allowed_backbones:
            raise ValueError('Backbone (\'{}\') not in allowed backbones ({}).'.format(backbone, MobileNetBackbone.allowed_backbones))
 Checks whether the backbone string is correct.
        
keras_retinanet/models/mobilenet.py