def validate(self):
        """ Checks whether the backbone string is correct.
        """
        allowed_backbones = ['seresnet18', 'seresnet34', 'seresnet50', 'seresnet101', 'seresnet152',
                             'seresnext50', 'seresnext101', 'senet154']
        backbone = self.backbone.split('_')[0]

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