docs: def handle_options():
      '''Handle options.
      '''
      parser = OptionParser()
      parser.set_defaults(add=False)
      parser.set_defaults(rhofile=False)
      parser.set_defaults(aniso=False)
  
      parser.add_option("-m",
                        dest="m",
                        type="float",
                        help="User override for coefficient m",
                        default=0.021,
                        )
      parser.add_option("-T",
                        dest="T_std",
                        type="float",
                        help="User override for standard temperature",
                        default=10.0,
                        )
      parser.add_option("--add",
                        help="add temperature effect, default=sub",
                        dest='add',
                        action='store_true',
                        default=False
                        )
      parser.add_option("--aniso",
                        help="resistivity data in anisotropic (three columns)",
                        dest='aniso',
                        action='store_true',
                        default=False
                        )
      # input options
      parser.add_option("--temp",
                        dest="temp_file",
                        help="file with temperature data",
                        metavar="file",
                        default='temp/tprofile.mag',
                        )
      parser.add_option("--filename",
                        dest='filename',
                        help='file with resistivity data',
                        metavar="file",
                        type='string',
                        default=None,
                        )
      parser.add_option('-r',
                        "--rho",
                        help="define input file as a rho-file, default=mag-file",
                        dest='rhofile',
                        action='store_true',
                        )
      # output options
      parser.add_option("-o",
                        "--output",
                        dest="output",
                        help="output file",
                        metavar="file",
                        default="temp/rho_T.mag",
                        )
  
      (options, args) = parser.parse_args()
      return options