:return: base model from Keras based on user-supplied model name

def _get_base_model(self):
        """
        :return: base model from Keras based on user-supplied model name
        """
        if self.model_name == 'inception_v3':
            return InceptionV3(weights='imagenet', include_top=False)
        elif self.model_name == 'xception':
            return Xception(weights='imagenet', include_top=False)
        elif self.model_name == 'vgg16':
            return VGG16(weights='imagenet', include_top=False)
        elif self.model_name == 'vgg19':
            return VGG19(weights='imagenet', include_top=False)
        elif self.model_name == 'resnet50':
            return ResNet50(weights='imagenet', include_top=False)
        else:
            raise ValueError('Cannot find base model %s' % self.model_name)