code: def resnet50(num_classes=1000, pretrained='imagenet'):
      
      model = models.resnet50(pretrained=False)
      if pretrained is not None:
          settings = pretrained_settings['resnet50'][pretrained]
          model = load_pretrained(model, num_classes, settings)
      model = modify_resnets(model)
      return model
docs: Constructs a ResNet-50 model.