Re: [PATCH 3/4] qemu-iotests: let "check" spawn an arbitrary test command

[Paolo Bonzini <pbonzini@redhat.com>]

On 23/03/21 17:43, Vladimir Sementsov-Ogievskiy wrote:
> 
> Interesting that REMAINDER documentation disappeared from latest (3.9) 
> python documentation https://docs.python.org/3.9/library/argparse.html , 
> but exists here https://docs.python.org/3.8/library/argparse.html  (and 
> no mark of deprecation)

Whoa.  https://bugs.python.org/issue17050 says:

---
Since this feature is buggy, and there isn't an easy fix, we should 
probably remove any mention of it from the docs.  We can still leave it 
as an undocumented legacy feature.

There is precedent for leaving `nargs` constants undocumented. 
`argparse.PARSER` ('+...') is used by the subparser mechanism, but is 
not documented.  https://bugs.python.org/issue16988
---

The problematic case appears to be when you have more than one 
positional argument, which is exactly the case with the 3.8 documented 
use of REMAINDER.  Hence the decision to drop the documentation.

However, "check" works fine because the REMAINDER argument is the only 
positional argument:

     $ ./check 001 -d
     Test "tests/-d" is not found

Another possibility is to pre-process sys.argv like this:

     if '--' in sys.argv:
         cmd = True
         args = sys.argv[0:sys.argv.index('--')]
         posargs = sys.argv[len(args)+1:]
     else:
         cmd = False
         args = list(x for x in sys.argv if x.startswith('-'))
         posargs = list(x for x in sys.argv if not x.startswith('-'))

But getting the help message right etc. would be messy.

Paolo