python argparse 无法传递bool

    parser = argparse.ArgumentParser()
    parser.add_argument(
        ‘–isTrain’,
        help=’Do you want to train the network?’,
        type=bool,
    )
args = parser.parse_args()
my_bool = args.bool_arg

def str2bool(v):
if v.lower() in ('yes', 'true', 't', 'y', '1'):
    return True
elif v.lower() in ('no', 'false', 'f', 'n', '0'):
    return False
else:
    raise argparse.ArgumentTypeError('Unsupported value encountered.')

if __name__ == '__main__':
parser = argparse.ArgumentParser()
parser.add_argument(
    '--isTrain',
    type= str2bool,
    nargs = '?', 
    const = True, 
    help='If this is a train process?')
args, unparsed = parser.parse_known_args()
if args.isTrain == False:
    isTrain = args.isTrain 
tf.app.run(main=main)