argparse fails to get value of argument if the value is --

[kushal-kumaran]

Bug report

Bug description:

This code:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("--broken")
parser.add_argument("--working")

args = parser.parse_args(["--broken=--", "--working=asdf"])
print(args)

prints:

$ podman run -v $(pwd):/src python:3.11.5-bookworm python /src/delim.py 
Namespace(broken=[], working='asdf')

The value of the --broken argument is not parsed, presumably because it is the standard end-of-argument-list value. But this does not seem expected when the value is introduced with =. Besides, in this case, the parsing does continue for subsequent args, so it was not actually treated as end of arguments.

CPython versions tested on:

3.11, 3.12

Operating systems tested on:

Linux

Linked PRs

• gh-109475: argument get the value is -- #110959
• gh-109475: Fix support of explicit option value "--" in argparse #114814
• [3.12] gh-109475: Fix support of explicit option value "--" in argparse (GH-114814) #115036
• [3.11] gh-109475: Fix support of explicit option value "--" in argparse (GH-114814) #115037

[sobolevn]

-- means a very specific thing in argument parsing, I don't think that it should be a value of any other argument. If you need this value somewhere in your program, you can use some alias: like --flag=doubledash

[SouSingh]

Hello @kushal-kumaran I try to run it on my device I get some output I hope that will help

[ericvsmith]

-- means a very specific thing in argument parsing, I don't think that it should be a value of any other argument. If you need this value somewhere in your program, you can use some alias: like --flag=doubledash

I completely disagree with this. Imagine if you were reading the documentation of a command line utility, and it said "If you want the output file to be named '--', then use 'doubledash' instead, and this will be translated to '--' internally. It is not possible to specify an output name of 'doubledash'."

I think this is a completely valid bug report. I'm not sure it's fixable, given all of the issues with argparse and how it scans arguments. I am surprised that using =-- doesn't work. See #53580 for a case where using = was suggested as a partial workaround.