Small inconsistency in usage message between the python and shell script versions of python-config

[kiendang]

BPO	45101
Nosy	@merwok, @kiendang
PRs	bpo-45101: Add consistency in usage message IO between 2 versions of python-config #28162

^{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 2021-09-04.18:32:12.094>
labels = ['type-bug', '3.11']
title = 'Small inconsistency in usage message between the python and shell script versions of python-config'
updated_at = <Date 2021-09-23.20:57:44.512>
user = 'https://github.com/kiendang'

bugs.python.org fields:

activity = <Date 2021-09-23.20:57:44.512>
actor = 'kiendang'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Demos and Tools']
creation = <Date 2021-09-04.18:32:12.094>
creator = 'kiendang'
dependencies = []
files = []
hgrepos = []
issue_num = 45101
keywords = ['patch']
message_count = 3.0
messages = ['401054', '401612', '402526']
nosy_count = 2.0
nosy_names = ['eric.araujo', 'kiendang']
pr_nums = ['28162']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue45101'
versions = ['Python 3.11']

[kiendang]

python-config outputs a usage instruction message in case either the --help option or invalid arguments are provided.

However there is a small different in the output I/O between the python and shell script versions of python-config. In the python version, the message always prints to stderr.

cpython/Misc/python-config.in

Lines 15 to 18 in bc1c49f

	def exit_with_usage(code=1):
	print("Usage: {0} [{1}]".format(
	sys.argv[0], '|'.join('--'+opt for opt in valid_opts)), file=sys.stderr)
	sys.exit(code)

def exit_with_usage(code=1):
    print("Usage: {0} [{1}]".format(
        sys.argv[0], '|'.join('--'+opt for opt in valid_opts)), file=sys.stderr)
    sys.exit(code)

while in the shell script version it always prints to stdout.

cpython/Misc/python-config.sh.in

Lines 5 to 9 in bc1c49f

	exit_with_usage ()
	{
	echo "Usage: $0 --prefix|--exec-prefix|--includes|--libs|--cflags|--ldflags|--extension-suffix|--help|--abiflags|--configdir|--embed"
	exit $1
	}

exit_with_usage ()
{
echo "Usage: $0 --prefix|--exec-prefix|--includes|--libs|--cflags|--ldflags|--extension-suffix|--help|--abiflags|--configdir|--embed"
exit $1
}

This inconsistency does not affect most users of python-config, who runs the script interactively. However it might cause issues when run programmatically.

[merwok]

I think python-config is modelled after pkg-config: what does the latter do?

Also, I’m not sure it would be appropriate to change behaviour in existing releases.

[kiendang]

Thanks. I didn't know about the pkg-config thing. I just checked with pkg-config on macOS

pkg-config --help prints usage instructions to stdout

pkg-config followed by invalid options prints output to stderr, for example pkg-config --asdf prints Unknown option --asdf to stderr.

The PR I submitted does something similar, making both python and shell script versions of python-config to print out the usage instruction message to stdout when --help is provided and stderr when given invalid arguments.