#16306: Fix multiple error messages when unknown command line parameters where passed to the interpreter. Patch by Hieu Nguyen.

Lib/test/test_cmd_line.py

@@ -6,7 +6,8 @@ import test.test_support
 import sys
 import unittest
 from test.script_helper import (
-    assert_python_ok, spawn_python, kill_python, python_exit_code
+    assert_python_ok, assert_python_failure, spawn_python, kill_python,
+    python_exit_code
 )
 
 
@@ -116,6 +117,14 @@ class CmdLineTest(unittest.TestCase):
         assert_python_ok(filename)
 
 
+    def test_unknown_options(self):
+        # Add "without='-E'" to prevent _assert_python append env_vars -E
+        # which changes the output of stderr
+        rc, out, err = assert_python_failure('-z', without='-E')
+        self.assertIn(b'Unknown option', err)
+        self.assertEqual(err.splitlines().count(b'Unknown option: -z'), 1)
+        self.assertEqual(b'', out)
+
 def test_main():
     test.test_support.run_unittest(CmdLineTest)
     test.test_support.reap_children()

Misc/ACKS

@@ -701,6 +701,7 @@ Tony Nelson
 Chad Netzer
 Max Neunhöffer
 George Neville-Neil
+Hieu Nguyen
 Johannes Nicolai
 Samuel Nicolary
 Gustavo Niemeyer

Misc/NEWS

@@ -9,6 +9,9 @@ What's New in Python 2.7.4
 Core and Builtins
 -----------------
 
+- Issue #16306: Fix multiple error messages when unknown command line
+  parameters where passed to the interpreter.  Patch by Hieu Nguyen.
+
 - Issue #15379: Fix passing of non-BMP characters as integers for the charmap
   decoder (already working as unicode strings).  Patch by Serhiy Storchaka.
 

Python/getopt.c

@@ -41,7 +41,7 @@ static char *opt_ptr = "";
 
 void _PyOS_ResetGetOpt(void)
 {
-    _PyOS_opterr = 1;
+    _PyOS_opterr = 0;   /* prevent printing the error in 2nd loop in main.c */
     _PyOS_optind = 1;
     _PyOS_optarg = NULL;
     opt_ptr = "";
@@ -90,11 +90,13 @@ int _PyOS_GetOpt(int argc, char **argv, char *optstring)
         return -1;
 
     if (option == 'J') {
+        if (_PyOS_opterr)
             fprintf(stderr, "-J is reserved for Jython\n");
         return '_';
     }
 
     if (option == 'X') {
+        if (_PyOS_opterr)
             fprintf(stderr,
                 "-X is reserved for implementation-specific arguments\n");
         return '_';