使用argparse的Python中的条件命令行参数

Question

我希望有一个带有--action=标志的程序，其中有效的选项是dump和upload，upload是缺省值。如果(且仅当)选择了dump，我希望还有一个--dump-format=选项。有没有办法用argparse来表达这一点，或者我需要接受所有的参数，然后自己做逻辑。

Answer 1

您可以使用parser.error

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--action', choices=['upload', 'dump'], default='dump')
parser.add_argument('--dump-format')
args = parser.parse_args()
if args.action != 'dump' and args.dump_format:
    parser.error('--dump-format can only be set when --action=dump.')

Answer 2

argparse模块提供了一种方法来实现这一点，而无需实现自己的需求检查。下面的例子使用“子解析器”或“子命令”。我为"dump“实现了一个子解析器，为"format”实现了一个子解析器。

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)

在命令行中如下所示：

$ 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
$ 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
$ 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：http://docs.python.org/dev/library/argparse.html#argparse.ArgumentParser.add_subparsers

Answer 3

另一种解决问题的方法是使用subcommands (a‘’la git)，并将"action“作为第一个参数：

script dump --dump-format="foo"
script upload