Index: Include/unicodeobject.h
===================================================================
--- Include/unicodeobject.h	(révision 84621)
+++ Include/unicodeobject.h	(copie de travail)
@@ -550,8 +550,14 @@
     register PyObject *obj      /* Object */
     );
 
-PyAPI_FUNC(PyObject *) PyUnicode_FromFormatV(const char*, va_list);
-PyAPI_FUNC(PyObject *) PyUnicode_FromFormat(const char*, ...);
+PyAPI_FUNC(PyObject *) PyUnicode_FromFormatV(
+    const char *format,   /* ASCII-encoded string  */
+    va_list vargs
+    );
+PyAPI_FUNC(PyObject *) PyUnicode_FromFormat(
+    const char *format,   /* ASCII-encoded string  */
+    ...
+    );
 
 /* Format the object based on the format_spec, as defined in PEP 3101
    (Advanced String Formatting). */
Index: Include/pyerrors.h
===================================================================
--- Include/pyerrors.h	(révision 84621)
+++ Include/pyerrors.h	(copie de travail)
@@ -183,7 +183,11 @@
     PyObject *, const Py_UNICODE *);
 #endif /* MS_WINDOWS */
 
-PyAPI_FUNC(PyObject *) PyErr_Format(PyObject *, const char *, ...);
+PyAPI_FUNC(PyObject *) PyErr_Format(
+    PyObject *exception,
+    const char *format,   /* ASCII-encoded string  */
+    ...
+    );
 
 #ifdef MS_WINDOWS
 PyAPI_FUNC(PyObject *) PyErr_SetFromWindowsErrWithFilenameObject(
Index: Objects/unicodeobject.c
===================================================================
--- Objects/unicodeobject.c	(révision 84621)
+++ Objects/unicodeobject.c	(copie de travail)
@@ -1102,7 +1102,15 @@
                 appendstring(p);
                 goto end;
             }
-        } else
+        }
+        else if (128 <= (unsigned char)*f) {
+            PyErr_Format(PyExc_ValueError,
+                "PyUnicode_FromFormatV() expects an ASCII-encoded format "
+                "string, got a non-ascii byte: 0x%02x",
+                *f);
+            goto fail;
+        }
+        else
             *s++ = *f;
     }
 
Index: Lib/test/test_unicode.py
===================================================================
--- Lib/test/test_unicode.py	(révision 84621)
+++ Lib/test/test_unicode.py	(copie de travail)
@@ -1385,7 +1385,19 @@
         self.assertEquals("%s" % s, '__str__ overridden')
         self.assertEquals("{}".format(s), '__str__ overridden')
 
+    def test_from_format(self):
+        # Ensure that PyUnicode_FromFormat() raises an error for a non-ascii
+        # format string.
+        from _testcapi import format_unicode
 
+        # ascii format, non-ascii argument
+        text = format_unicode(b'ascii\x7f=%U', 'unicode\xe9')
+        self.assertEqual(text, 'ascii\x7f=unicode\xe9')
+
+        # non-ascii format, ascii argument
+        self.assertRaises(ValueError,
+            format_unicode, b'unicode\xe9=%s', 'ascii')
+
 def test_main():
     support.run_unittest(__name__)
 
Index: Modules/_testcapimodule.c
===================================================================
--- Modules/_testcapimodule.c	(révision 84621)
+++ Modules/_testcapimodule.c	(copie de travail)
@@ -2193,6 +2193,17 @@
     return NULL;
 }
 
+static PyObject *
+format_unicode(PyObject *self, PyObject *args)
+{
+    const char *format;
+    PyObject *arg;
+    if (!PyArg_ParseTuple(args, "yU", &format, &arg))
+        return NULL;
+    return PyUnicode_FromFormat(format, arg);
+
+}
+
 static PyMethodDef TestMethods[] = {
     {"raise_exception",         raise_exception,                 METH_VARARGS},
     {"raise_memoryerror",   (PyCFunction)raise_memoryerror,  METH_NOARGS},
@@ -2272,6 +2283,7 @@
     {"make_exception_with_doc", (PyCFunction)make_exception_with_doc,
      METH_VARARGS | METH_KEYWORDS},
     {"crash_no_current_thread", (PyCFunction)crash_no_current_thread, METH_NOARGS},
+    {"format_unicode", format_unicode, METH_VARARGS},
     {NULL, NULL} /* sentinel */
 };