Don't parse options after the last positional

问题:

I'm writing a wrapper around the ssh command line client. After the first positional argument that's part of command, all further options should also be treated as positional arguments.

Under optparse, I believe this would be done with disable_interspersed_args.

Presently I have something like this:

parser = argparse.ArgumentParser()
parser.add_argument('--parallel', default=False, action='store_true')
# maybe allow no command? this would ssh interactively into each machine...
parser.add_argument('command', nargs='+')
args = parser.parse_args()

But if options are passed as part of the command (such as my_wrapper ls -l), they're instead interpreted by ArgumentParser as unknown options. error: unrecognized arguments: -l

If I use parse_known_args(), the options may be taken out of order.

p = argparse.ArgumentParser()
p.add_argument('-a', action='store_true')
p.add_argument('command', nargs='+')
print(p.parse_known_args())

$ python3 bah.py -b ls -l -a
(Namespace(a=True, command=['ls']), ['-b', '-l'])

Here you can see that -b's position before ls has been lost, and -a has been parsed out from the command, which is not desired.

How can I:

• Prevent arguments from being parsed after a certain point?
• Disable parsing of interspersed arguments?
• Allow arguments with a prefix to be consumed as positional arguments?

回答1:

I had the same problem. I found the solution on the argparse bug tracker: http://code.google.com/p/argparse/issues/detail?id=52

The solution is simple: replace nargs='+' (or '*') with nargs=argparse.REMAINDER. This special value is not documented, but it does what you want.

回答2:

I think your best bet to start solving these issues is to try out -- after all your optional args. -- is a pseudo-arg that tells ArgumentParser that everything after is a positional argument. Docs are here

As for prevent arguments from being parsed after a certain point, you can pass part of argv to parse_args. That combined with some introspection can be used to limit what is parsed.

回答3:

Another option is to use parse_known_args, which stops parsing when an unknown argument is encountered.