Index: Python/pythonrun.c
===================================================================
--- Python/pythonrun.c	(révision 67973)
+++ Python/pythonrun.c	(copie de travail)
@@ -84,6 +84,7 @@
 int Py_FrozenFlag; /* Needed by getpath.c */
 int Py_IgnoreEnvironmentFlag; /* e.g. PYTHONPATH, PYTHONHOME */
 int Py_NoUserSiteDirectory = 0; /* for -s and site.py */
+int Py_UnbufferedStdoutFlag = 0; /* Unbuffered binary std{out,err} */
 
 /* PyModule_GetWarningsModule is no longer necessary as of 2.6
 since _warnings is builtin.  This API should not be used. */
@@ -259,7 +260,7 @@
 
 	if (install_sigs)
 		initsigs(); /* Signal handling stuff, including initintr() */
-		
+
 	/* Initialize warnings. */
 	_PyWarnings_Init();
 	if (PySys_HasWarnOptions()) {
@@ -724,6 +725,49 @@
 	}
 }
 
+static PyObject*
+create_stdio(int fd, char* name, char* encoding, char* errors)
+{
+	PyObject *io = NULL, *buf = NULL, *stream = NULL, *mode = NULL;
+
+	if (!Py_UnbufferedStdoutFlag) {
+		return PyFile_FromFd(fd, name, "w",
+				-1,
+				encoding, errors, "\n", 0);
+	}
+
+	io = PyImport_ImportModule("io");
+	if (io == NULL)
+		goto error;
+
+	buf = PyObject_CallMethod(io, "open", "isiOOOi",
+				  fd, "wb", 0,
+				  Py_None, Py_None, Py_None, 0);
+	if (buf == NULL)
+		goto error;
+
+	stream = PyObject_CallMethod(io, "TextIOWrapper", "OsssO",
+				     buf, encoding, errors,
+				     "\n", Py_True);
+	Py_CLEAR(io);
+	Py_CLEAR(buf);
+	if (stream == NULL)
+		goto error;
+
+	mode = PyUnicode_FromString("w");
+	if (!mode || PyObject_SetAttrString(stream, "mode", mode) < 0)
+		goto error;
+	Py_CLEAR(mode);
+	return stream;
+
+error:
+	Py_XDECREF(io);
+	Py_XDECREF(buf);
+	Py_XDECREF(stream);
+	Py_XDECREF(mode);
+	return NULL;
+}
+
 /* Initialize sys.stdin, stdout, stderr and builtins.open */
 static int
 initstdio(void)
@@ -790,7 +834,7 @@
 #endif
 	}
 	else {
-		if (!(std = PyFile_FromFd(fd, "<stdin>", "r", -1, encoding, 
+		if (!(std = PyFile_FromFd(fd, "<stdin>", "r", -1, encoding,
 					  errors, "\n", 0))) {
 			goto error;
 		}
@@ -810,8 +854,7 @@
 #endif
 	}
 	else {
-		if (!(std = PyFile_FromFd(fd, "<stdout>", "w", -1, encoding, 
-					  errors, "\n", 0))) {
+		if (!(std = create_stdio(fd, "<stdout>", encoding, errors))) {
 			goto error;
 		}
 	} /* if (fd < 0) */
@@ -831,8 +874,7 @@
 #endif
 	}
 	else {
-		if (!(std = PyFile_FromFd(fd, "<stderr>", "w", -1, encoding,
-					  "backslashreplace", "\n", 0))) {
+		if (!(std = create_stdio(fd, "<stderr>", encoding, "backslashreplace"))) {
 			goto error;
 		}
 	} /* if (fd < 0) */
@@ -2036,7 +2078,7 @@
 		alloca(PYOS_STACK_MARGIN * sizeof(void*));
 		return 0;
 	} __except (GetExceptionCode() == STATUS_STACK_OVERFLOW ?
-			EXCEPTION_EXECUTE_HANDLER : 
+			EXCEPTION_EXECUTE_HANDLER :
 			EXCEPTION_CONTINUE_SEARCH) {
 		int errcode = _resetstkoflw();
 		if (errcode == 0)
Index: Include/pydebug.h
===================================================================
--- Include/pydebug.h	(révision 67973)
+++ Include/pydebug.h	(copie de travail)
@@ -18,6 +18,7 @@
 PyAPI_DATA(int) Py_DivisionWarningFlag;
 PyAPI_DATA(int) Py_DontWriteBytecodeFlag;
 PyAPI_DATA(int) Py_NoUserSiteDirectory;
+PyAPI_DATA(int) Py_UnbufferedStdoutFlag;
 
 /* this is a wrapper around getenv() that pays attention to
    Py_IgnoreEnvironmentFlag.  It should be used for getting variables like
Index: Lib/test/test_cmd_line.py
===================================================================
--- Lib/test/test_cmd_line.py	(révision 67973)
+++ Lib/test/test_cmd_line.py	(copie de travail)
@@ -142,7 +142,24 @@
                 self.exit_code('-c', command),
                 0)
 
+    def test_unbuffered(self):
+        # Test expected operation of the '-u' switch
+        for stream in ('stdout', 'stderr'):
+            # Binary is unbuffered
+            code = ("import os, sys; sys.%s.buffer.write(b'x'); os._exit(0)"
+                % stream)
+            data, rc = self.start_python_and_exit_code('-u', '-c', code)
+            self.assertEqual(rc, 0)
+            self.assertEqual(data, b'x', "binary %s not unbuffered" % stream)
+            # Text is line-buffered
+            code = ("import os, sys; sys.%s.write('x\\n'); os._exit(0)"
+                % stream)
+            data, rc = self.start_python_and_exit_code('-u', '-c', code)
+            self.assertEqual(rc, 0)
+            self.assertEqual(data.strip(), b'x',
+                "text %s not line-buffered" % stream)
 
+
 def test_main():
     test.support.run_unittest(CmdLineTest)
     test.support.reap_children()
Index: Modules/main.c
===================================================================
--- Modules/main.c	(révision 67973)
+++ Modules/main.c	(copie de travail)
@@ -292,7 +292,6 @@
 	wchar_t *module = NULL;
 	FILE *fp = stdin;
 	char *p;
-	int unbuffered = 0;
 	int skipfirstline = 0;
 	int stdin_is_interactive = 0;
 	int help = 0;
@@ -374,7 +373,7 @@
 			break;
 
 		case 'u':
-			unbuffered++;
+			Py_UnbufferedStdoutFlag++;
 			saw_unbuffered_flag = 1;
 			break;
 
@@ -423,7 +422,7 @@
 		Py_InspectFlag = 1;
 	if (!saw_unbuffered_flag &&
 	    (p = Py_GETENV("PYTHONUNBUFFERED")) && *p != '\0')
-		unbuffered = 1;
+		Py_UnbufferedStdoutFlag = 1;
 
 	if (!Py_NoUserSiteDirectory &&
 	    (p = Py_GETENV("PYTHONNOUSERSITE")) && *p != '\0')
@@ -444,7 +443,7 @@
 
 	stdin_is_interactive = Py_FdIsInteractive(stdin, (char *)0);
 
-	if (unbuffered) {
+	if (Py_UnbufferedStdoutFlag) {
 #if defined(MS_WINDOWS) || defined(__CYGWIN__)
 		_setmode(fileno(stdin), O_BINARY);
 		_setmode(fileno(stdout), O_BINARY);