Make getopt error message style more consistent

[9cel]

Fixes this minor inconsistency:

➜  cpython git:(consistent-getopt-errors) python3 -a
Unknown option: -a

vs.

➜  cpython git:(consistent-getopt-errors) python3 --a
unknown option --a

[cpython-cla-bot]

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[StanFromIreland]

Consistent with the launcher.

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[picnixz]

I can agree with making the error message consistent but I wonder if there's any chance we break CI parsing the output of the module in case of an error. While getopt is currently marked as deprecated, there are talks about considering it non-deprecated #126180 so the module could become active again. In addition, for users coming from C, getopt is usually easier to use since it's almost identitcal to getopt.h, so the module might be still in use in the wild.

If we accept changing the error message, we should probably make a NEWS entry (and perhaps a What's New entry) just so that users are notified, even if there's only one user (and in this case, this requires an issue). cc @serhiy-storchaka

[serhiy-storchaka]

This is not related to the getopt module. This is emitted from a local copy of getopt.c. Error messages are different from error messages in GNU getopt.c and getopt.py:

$ LC_ALL=C ls -z
ls: invalid option -- 'z'
Try 'ls --help' for more information.
$ LC_ALL=C ls --y
ls: unrecognized option '--y'
Try 'ls --help' for more information.

$ ./python -m quopri -z
option -z not recognized
usage: quopri [-t | -d] [file] ...
-t: quote tabs
-d: decode; default encode
$ ./python -m quopri --z
option --z not recognized
usage: quopri [-t | -d] [file] ...
-t: quote tabs
-d: decode; default encode

So there is no single correct variant.

But error messages starting with a lower-case were introduced not so long ago in 42aa93b (bpo-31650). Error messages starting with an upper-case were here from the beginning. So we can assume that it was an error in 42aa93b.

cc @benjaminp