Clarify %(prog)s in argparse help formatter returns basename of sys.argv[0] by default

[py-user]

BPO	27992
Nosy	@rhettinger, @py-user, @tirkarthi
PRs	bpo-27992: Clarify %(prog)s in argparse help formatter for sys.argv[0] #12717
Files	argparse_sys-argv-0-part.diff: Specifies term argparse_sys-argv-0-basename.diff: Specifies term to basename

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-09-07.03:10:52.945>
labels = ['3.7', '3.8', 'type-bug', 'library', 'docs']
title = 'Clarify %(prog)s in argparse help formatter returns basename of sys.argv[0] by default'
updated_at = <Date 2019-10-24.08:47:12.535>
user = 'https://github.com/py-user'

bugs.python.org fields:

activity = <Date 2019-10-24.08:47:12.535>
actor = 'xtreak'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'Library (Lib)']
creation = <Date 2016-09-07.03:10:52.945>
creator = 'py.user'
dependencies = []
files = ['44420', '48245']
hgrepos = []
issue_num = 27992
keywords = ['patch']
message_count = 4.0
messages = ['274729', '339287', '339557', '339558']
nosy_count = 5.0
nosy_names = ['rhettinger', 'docs@python', 'py.user', 'paul.j3', 'xtreak']
pr_nums = ['12717']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27992'
versions = ['Python 3.7', 'Python 3.8']

[py-user]

https://docs.python.org/3/library/argparse.html#argumentparser-objects
"prog - The name of the program (default: sys.argv[0])"

It doesn't take all sys.argv[0]. It splits sys.argv[0] and takes only the trailing part.

An example:

a.py

#!/usr/bin/env python3

import argparse
import sys

parser = argparse.ArgumentParser()
parser.add_argument("arg", help="The name is %(prog)s, the sys.argv[0] is " + sys.argv[0])
args = parser.parse_args()

The output in the console:

[guest@localhost bugs]$ ../bugs/a.py -h
usage: a.py [-h] arg

positional arguments:
arg The name is a.py and sys.argv[0] is ../bugs/a.py

optional arguments:
-h, --help show this help message and exit
[guest@localhost bugs]$

In the output we see that %(prog)s takes only trailing part of sys.argv[0] not all.

Applied a patch to the issue that specifies about part of sys.argv[0].

[tirkarthi]

Thanks for the report. To be little more clear it returns the "basename of sys.argv[0]" at [0] than the attached patch that says "uses part of sys.argv[0]" .

[0]

cpython/Lib/argparse.py

Line 1638 in 62f9588

prog = _os.path.basename(_sys.argv[0])

[py-user]

@Karthikeyan Singaravelan
Thank you for the point. I added a new patch.

[tirkarthi]

CPython now accepts GitHub PRs. Please see the workflow at https://devguide.python.org . You can raise a PR against master branch.

[slateny]

Resolved per #30298