Python 中使用 argparse 的条件命令行参数

我想要一个程序，需要--action=标志，其中有效选择是dump and upload, with upload是默认值。如果（且仅当）dump已选择，我希望还有一个--dump-format=选项。有没有办法使用 argparse 来表达这一点，或者我是否需要接受所有参数并自己执行逻辑。

argparse 模块提供了一种无需实现您自己的方法即可执行此操作的方法 必要性检查。下面的示例使用“子解析器”或“子命令”。 我已经实现了一个用于“转储”的子解析器和一个用于“格式”的子解析器。

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('file', help='The file you want to act on.')
subparsers = parser.add_subparsers(dest='subcommand')
subparsers.required = True  # required since 3.7

#  subparser for dump
parser_dump = subparsers.add_parser('dump')
# add a required argument
parser_dump.add_argument(
    'format',
    choices=['csv', 'json'],
    help='Dump the file in this format.')

#  subparser for upload
parser_upload = subparsers.add_parser('upload')
# add a required argument
parser_upload.add_argument(
    'server',
    choices=['amazon', 'imgur'],
    help='Upload the file to this service.')

args = parser.parse_args()
print args
if args.subcommand == 'dump':
    print 'I will now dump "%s" in the %s format' % (args.file, args.format)
if args.subcommand == 'upload':
    print 'I will now upload "%s" to %s' % (args.file, args.server)

在命令行上看起来像这样：

$ python ap.py 
usage: ap.py [-h] file {upload,dump} ...
ap.py: error: too few arguments

$ python ap.py tmp.txt 
usage: ap.py [-h] file {upload,dump} ...
ap.py: error: too few arguments

Upload:

$ python ap.py tmp.txt upload
usage: ap.py file upload [-h] {amazon,imgur}
ap.py file upload: error: too few arguments

$ python ap.py tmp.txt upload amazo
usage: ap.py file upload [-h] {amazon,imgur}
ap.py file upload: error: argument server: invalid choice: 'amazo' (choose from 'amazon', 'imgur')

$ python ap.py tmp.txt upload amazon
Namespace(file='tmp.txt', server='amazon', subcommand='upload')
I will now upload "tmp.txt" to amazon

$ python ap.py tmp.txt upload imgur
Namespace(file='tmp.txt', server='imgur', subcommand='upload')
I will now upload "tmp.txt" to imgur

Dump:

$ python ap.py tmp.txt dump
usage: ap.py file dump [-h] {csv,json}
ap.py file dump: error: too few arguments

$ python ap.py tmp.txt dump csv
Namespace(file='tmp.txt', format='csv', subcommand='dump')
I will now dump "tmp.txt" in the csv format

$ python ap.py tmp.txt dump json
Namespace(file='tmp.txt', format='json', subcommand='dump')
I will now dump "tmp.txt" in the json format

更多信息：ArgumentParser.add_subparsers() http://docs.python.org/library/argparse.html#argparse.ArgumentParser.add_subparsers