[issue37510] argparse removing more "--" than it should
New submission from Jorge L. Martinez :
$ python -c '
import argparse
p = argparse.ArgumentParser()
p.add_argument("first_arg")
p.add_argument("args", nargs="*")
r = p.parse_args(["foo", "--", "bar", "--", "baz", "--", "zap"])
print(r.first_arg + " " + " ".join(r.args))
'
returns:
foo bar baz -- zap
when I think it should return:
foo bar -- baz -- zap
--
components: Library (Lib)
messages: 347378
nosy: jol
priority: normal
severity: normal
status: open
title: argparse removing more "--" than it should
type: behavior
versions: Python 3.7
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[issue37510] argparse removing more "--" than it should
Jorge L. Martinez added the comment: Sorry, I forgot to add details on my machine. Python: 3.7.3 OS: Archlinux -- ___ Python tracker <https://bugs.python.org/issue37510> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue37510] argparse removing more "--" than it should
Jorge L. Martinez added the comment: To be clear, my opinion is that a single call of parse_args() should only ever remove the first "--". Right now, it seems that it removes the first of each argument group, as determined by nargs, I guess. -- ___ Python tracker <https://bugs.python.org/issue37510> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue37510] argparse removing more "--" than it should
Jorge L. Martinez added the comment:
> There are earlier bug/issues about the '--'.
Yes, there are:
https://bugs.python.org/issue9571
https://bugs.python.org/issue3
https://bugs.python.org/issue14364
But this one seems separate. Though they're related, they don't seem like
duplicates, so that's why I thought I'd make this one.
> Also look at the parser code itself. Keep in mind that parsing is done in
> two passes - once to identify flags versus arguments ('O/A') and then to
> allocate strings to arguments. I don't recall when '--' is being handled,
> possibly in both.
I'm not sure what your point is here. I did take a quick look at the code,
yesterday. I think the identification part you mention is done right. It marks
'O/A' as you mention. Then, when it sees "--", it marks it "-", and the rest of
the arguments are marked as "A".
I didn't look at the start of the code of the second pass or how it is
concretely linked to the first pass. However, I did see that in the example I
gave, _get_values() in argparse.py gets called twice (apparently once per
argument group as determined by nargs, I guess) to remove the "--" present in
arg_strings. The first time, arg_strings is ["foo", "--"] and the second time
it's ["bar", "--", "baz", "--", "zap"].
So, that's what happens, and where part of the fix should probably be. I don't
think the removal of "--" should happen in a function that gets called multiple
times. Though I didn't spend the time to see where the code should be
positioned, I can only imagine the correct behavior would be to remove the
argument marked as "-" by the first pass mentioned.
I didn't mention this yesterday, because I figured there wouldn't be much value
in sharing incomplete research like this, as opposed to a patch. I didn't want
to influence the work of whoever chose to invest time in this for a proper fix.
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[issue37510] argparse removing more "--" than it should
Jorge L. Martinez added the comment: > to remove the "--" present in arg_strings *to remove the first "--" present... -- ___ Python tracker <https://bugs.python.org/issue37510> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue37510] argparse removing more "--" than it should
Jorge L. Martinez added the comment: Maybe I can find the time to make a patch this weekend (either today or tomorrow). I hope I'm not underestimating this somehow, but I don't think this would take too long. The only issue I can foresee is in disagreement of what the correct behavior should be, which is why I gave my opinion that a single call of parse_args() should only ever remove a single "--". If I don't submit a patch by Monday (PDT), everyone should assume I decided not to tackle this. By the way, does this issue tracking platform support submitting to the issue thread by email? Maybe, I'll try that. -- ___ Python tracker <https://bugs.python.org/issue37510> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
