code: def export_obj(surface, file_name, **kwargs):
      
      content = export_obj_str(surface, **kwargs)
      return exch.write_file(file_name, content)
docs: Exports surface(s) as a .obj file.
  
      Keyword Arguments:
          * ``vertex_spacing``: size of the triangle edge in terms of surface points sampled. *Default: 2*
          * ``vertex_normals``: if True, then computes vertex normals. *Default: False*
          * ``parametric_vertices``: if True, then adds parameter space vertices. *Default: False*
          * ``update_delta``: use multi-surface evaluation delta for all surfaces. *Default: True*
  
      :param surface: surface or surfaces to be saved
      :type surface: abstract.Surface or multi.SurfaceContainer
      :param file_name: name of the output file
      :type file_name: str
      :raises GeomdlException: an error occurred writing the file