code: def _get_base_model(self):
          
          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)
docs: :return: base model from Keras based on user-supplied model name