argparse: How to separate unknown(and optional) args when subparsers are present.(subparsers are also optional)

Question

I have the following code

parser = argparse.ArgumentParser(allow_abbrev=False, add_help=False)
parser.add_argument('--conf', nargs=1)
parser.add_argument('-h', '--help', nargs='?', const='generic')
parser.add_argument('-v', '--version', action="store_true")

subparsers = parser.add_subparsers()
subparsers.required = False
parser_start = subparsers.add_parser('start')
group1 = parser_start.add_mutually_exclusive_group()
group1.add_argument('--quiet', action="store_true")
group1.add_argument('-V', '--verbose', nargs="*")

# parser_console = subparsers.add_parser('console')

print(argv)
parsed_args = parser.parse_known_args(argv)

Now, when I pass argv as argv = ['abc', 'def'] or argv = ['abc']

I get

['abc', 'def']
usage: lbrynet [--conf CONF] [-h [HELP]] [-v] {start} ...
lbrynet: error: invalid choice: 'abc' (choose from 'start')

What I was expecting was to get ['abc', 'def'] in the tuple for unknown args. I've checked a lot of stackoverflow answers(such as ans 1 , ans 2 , ans 3 , ans 4 ) and bug reports(eg br 1 ) and a lot but I can't seem to find a way to do it. Is this an unsolved bug? Am I wrong in expecting that this can be done. If this can't be done are there any workarounds to doing this?

Also to clarify, the ['abc', 'def'] got from the tuple have to be passed to some other function to be processed.

Happy to provide any further clarifications and/or clear any ambiguities.

Answer 1

As I wrote in a comment, subparsers is a positional argument.

To illustrate with a plain positional:

In [307]: parser = argparse.ArgumentParser()
In [308]: a1 = parser.add_argument('foo')

In [309]: parser.parse_known_args(['one','two'])
Out[309]: (Namespace(foo='one'), ['two'])

'one' is allocated to the first positional. Now give foo choices:

In [310]: a1.choices = ['bar','test']
In [311]: parser.parse_known_args(['one','two'])
usage: ipython3 [-h] {bar,test}
ipython3: error: argument foo: invalid choice: 'one' (choose from 'bar', 'test')

It is still trying to allocate the first string to foo . Since it doesn't match choices , it raises an error.

In [312]: parser.parse_known_args(['bar','one','two'])
Out[312]: (Namespace(foo='bar'), ['one', 'two'])

Strings are assigned to positionals based on position, not on value. Any value checking, such as with type or choices is done after assignment.

Change the choices to a type test:

In [313]: a1.choices = None
In [314]: a1.type = int
In [315]: parser.parse_known_args(['bar','one','two'])
usage: ipython3 [-h] foo
ipython3: error: argument foo: invalid int value: 'bar'

In [316]: parser.parse_known_args(['12','one','two'])
Out[316]: (Namespace(foo=12), ['one', 'two'])