Make the Python CLI error message style more consistent (GH-128129)

Author: 9cel

Lib/test/test_cmd_line.py

@@ -1012,7 +1012,7 @@ def test_parsing_error(self):
                               stdout=subprocess.PIPE,
                               stderr=subprocess.PIPE,
                               text=True)
-        err_msg = "unknown option --unknown-option\nusage: "
+        err_msg = "Unknown option: --unknown-option\nusage: "
         self.assertTrue(proc.stderr.startswith(err_msg), proc.stderr)
         self.assertNotEqual(proc.returncode, 0)
 

Python/getopt.c

@@ -102,7 +102,7 @@ int _PyOS_GetOpt(Py_ssize_t argc, wchar_t * const *argv, int *longindex)
         // Parse long option.
         if (*opt_ptr == L'\0') {
             if (_PyOS_opterr) {
-                fprintf(stderr, "expected long option\n");
+                fprintf(stderr, "Expected long option\n");
             }
             return -1;
         }
@@ -114,7 +114,7 @@ int _PyOS_GetOpt(Py_ssize_t argc, wchar_t * const *argv, int *longindex)
         }
         if (!opt->name) {
             if (_PyOS_opterr) {
-                fprintf(stderr, "unknown option %ls\n", argv[_PyOS_optind - 1]);
+                fprintf(stderr, "Unknown option: %ls\n", argv[_PyOS_optind - 1]);
             }
             return '_';
         }