code: def _get_model_metadata(model_class, metadata, version=None):
      
      from turicreate import __version__
      info = {
          'turicreate_version': __version__,
          'type': model_class,
      }
      if version is not None:
          info['version'] = str(version)
      info.update(metadata)
      return info
docs: Returns user-defined metadata, making sure information all models should 
      have is also available, as a dictionary