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pdb: -- argument separator is rejected #148615
Description
Bug report
Bug description:
When using python -m pdb, it is impossible to pass arguments that share names with pdb flags (such as -c) to the target script:
python3 -m pdb -- script.py ...
Standard argparse behavior dictates using -- to separate parser arguments from script arguments, but pdb currently intercepts -- and crashes.
In old versions of Python (3.9) that used getopt for parsing, -- worked fine.
It seems to have regressed in Python 3.13, and #140933 does not fix it.
Reproducer
# Attempt to pass '-c' to the target script using '--'
python3 -m pdb -c continue -- my_script.py -c exampleExpected behavior
pdb starts debugging my_script.py with sys.argv = ['my_script.py', '-c', "example"].
Actual behavior
usage: python3 -m pdb [-h] [-c command] (-m module | -p pid | pyfile) [args ...]
python3 -m pdb: error: unrecognized arguments: --
This is triggered by the following branch
elif args[0].startswith('-'):
# Invalid argument before the script name.
invalid_args = list(itertools.takewhile(lambda a: a.startswith('-'), args))
parser.error(f"unrecognized arguments: {' '.join(invalid_args)}")that branch could possibly do something like:
elif args[0].startswith('-'):
if args[0] == '--':
args.pop(0) # Discard the separator
if not args:
parser.error("missing script or module to run")
else:
# Invalid argument before the script name.
invalid_args = list(itertools.takewhile(lambda a: a.startswith('-'), args))
parser.error(f"unrecognized arguments: {' '.join(invalid_args)}")CPython versions tested on:
3.13, 3.14, 3.15, CPython main branch
Operating systems tested on:
Linux
Activity
picnixz commentedon Apr 15, 2026
cc @gaogaotiantian
Shrey-N commentedon Apr 15, 2026
Hiya, I think you are right, this is a regression from the argparse switch in pdb added in PR gh-125115. since the pdb parser has no positional arguments defined,
parser.parse_known_args()doesn't consume the -- separator and returns it in the remainder list. The manual post processing logic inparse_args()then incorrectly treats this -- as an unrecognized arg.I am working on a fix in
parse_args()that checks for the -- separator. When found it would be popped from the argument list to mark the end of debugger options. :)gh-148615: Handle `--` separator in pdb argument parsing (#148624)
[3.14] gh-148615: Handle `--` separator in pdb argument parsing (GH-1… (