Handle options.

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