i have an ArgumentParser with sub-parsers. Some flags are common for all sub-parsers, and I would like to be able to specify them either before or after the sub-command, or even mix before and after (at the user’s discretion).

Something like this:

$ ./test -v
Namespace(v=1)
$ ./test.py test -vv
Namespace(v=2)
$ ./test.py -vvv test
Namespace(v=3)
$ ./test.py -vv test -vv
Namespace(v=4)

So I tried something like this:

#!/usr/bin/env python3

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("-v", action="count")

subparsers = parser.add_subparsers()
sub = subparsers.add_parser("test")
sub.add_argument("-v", action="count")

print(parser.parse_args())

Running this program “test.py” gives me:

 ./test.py -h
usage: test.py [-h] [-v] {test} ...

positional arguments:
  {test}

options:
  -h, --help  show this help message and exit
  -v

$ ./test.py test -h
usage: test.py test [-h] [-v]

options:
  -h, --help  show this help message and exit
  -v

$ ./test.py -v
Namespace(v=1)

$ ./test.py test -vv
Namespace(v=2)

cool.

but it also gives me:

$ ./test.py -vvv test
Namespace(v=None)
$ ./test.py -vv test -vv
Namespace(v=2)

less cool 🙁

I also tried to specify parent-parsers explicitly:

common = argparse.ArgumentParser(add_help=False)
common.add_argument("-v", action="count")

parser = argparse.ArgumentParser(parents=[common])
sub = parser.add_subparsers().add_parser("test", parents=[common])

print(parser.parse_args())

but the result is the same.

So, I guess that as soon as the test subparser kicks in, it resets the value if v to None.

How do I prevent this?

(I notice that How can I define global options with sub-parsers in python argparse? is similar, and the answer there suggests to use different dest variables for the top-level and the sub-level parser. i would like to avoid that…)