Issue #3798: Write sys.exit() message to sys.stderr to use stderr encoding and

error handler, instead of writing to the C stderr file in utf-8

Lib/test/test_sys.py

@@ -178,6 +178,26 @@ class SysModuleTest(unittest.TestCase):
                               "raise SystemExit(47)"])
         self.assertEqual(rc, 47)
 
+        def check_exit_message(code, expected, env=None):
+            process = subprocess.Popen([sys.executable, "-c", code],
+                                       stderr=subprocess.PIPE, env=env)
+            stdout, stderr = process.communicate()
+            self.assertEqual(process.returncode, 1)
+            self.assertTrue(stderr.startswith(expected),
+                "%s doesn't start with %s" % (repr(stderr), repr(expected)))
+
+        # test that stderr buffer if flushed before the exit message is written
+        # into stderr
+        check_exit_message(
+            r'import sys; sys.stderr.write("unflushed,"); sys.exit("message")',
+            b"unflushed,message")
+
+        # test that the unicode message is encoded to the stderr encoding
+        env = os.environ.copy()
+        env['PYTHONIOENCODING'] = 'latin-1'
+        check_exit_message(
+            r'import sys; sys.exit(u"h\xe9")',
+            b"h\xe9", env=env)
 
     def test_getdefaultencoding(self):
         if test.test_support.have_unicode:

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 2.7 Release Candidate 1?
 Core and Builtins
 -----------------
 
+- Issue #3798: Write sys.exit() message to sys.stderr to use stderr encoding
+  and error handler, instead of writing to the C stderr file in utf-8
+
 - Issue #7902: When using explicit relative import syntax, don't try implicit
   relative import semantics.
 

Python/pythonrun.c

@@ -1106,7 +1106,13 @@ handle_system_exit(void)
     if (PyInt_Check(value))
         exitcode = (int)PyInt_AsLong(value);
     else {
-        PyObject_Print(value, stderr, Py_PRINT_RAW);
+        PyObject *sys_stderr = PySys_GetObject("stderr");
+        if (sys_stderr != NULL && sys_stderr != Py_None) {
+            PyFile_WriteObject(value, sys_stderr, Py_PRINT_RAW);
+        } else {
+            PyObject_Print(value, stderr, Py_PRINT_RAW);
+            fflush(stderr);
+        }
         PySys_WriteStderr("\n");
         exitcode = 1;
     }