Python argparse treat arguments in different ways

Question

I want to create an optional argument, which will be the '-- ' (double dash and a space) and get everything after it as its value. The problem is that some other optional arguments might appear after '-- '. I don't want these to be parsed as optional arguments, but as the values of '-- '. For example:

python prog1 --foo 1 --bar 2

Here foo and bar are optional arguments with values 1 and 2 respectively

python prog1 --foo 1 --bar 2 -- --foo 4 --bar 14

Here I want foo and bar that come before '-- ' to be parsed as optional arguments. But I want '--foo 4 --bar 14' to be parsed as the value of the optional argument '-- '. I would like to do this without renaming the parameters that come after '-- ' to foo2 and bar2, if possible.

So is this possible? And how could this be implemented?

Answer 1

argparse already supports -- as an end-of-options terminator. The only difference is that the default handling treats the following arguments individually. Suppose prog1 simply looks like

import argparse

p = argparse.ArgumentParser()

p.add_argument('--foo')
p.add_argument('--bar')
p.add_argument('remaining', nargs=argparse.REMAINDER)

print p.parse_args()

Then the command

% python prog1 --foo 1 --bar 2 -- --foo 4 --bar 14

produces

Namespace(bar='2', foo='1', remaining=['--', '--foo', '4', '--bar', '14'])

(rather than Namespace(..., remaining='-- --foo 4 --bar 14')). Than can be fixed with a quick post-processing step, if necessary:

args = p.parse_args()
args.remaining = " ".join(args.remaining)
print args

Then the result is

Namespace(bar='2', foo='1', remaining='-- --foo 4 --bar 14')

Discarding the -- argument requires some additional post-processing:

args = p.parse_args()
if args.remaining[0] == "--":
    args = args[1:]

Answer 2

It looks like the docopt library can do this for you;

From the usage-pattern-format section:

"[--]". Double dash "--" is used by convention to separate positional arguments that can be mistaken for options. In order to support this convention add "[--]" to your usage patterns.