Index: Python/_warnings.c
===================================================================
--- Python/_warnings.c	(revision 62464)
+++ Python/_warnings.c	(working copy)
@@ -732,6 +732,15 @@
 }
 
 
+int
+PyErr_WarnPy3k(const char *text, Py_ssize_t stacklevel)
+{
+    if (Py_Py3kWarningFlag)
+        return PyErr_WarnEx(PyExc_DeprecationWarning, text, stacklevel);
+    return 0;
+}
+
+
 PyDoc_STRVAR(warn_doc,
 "Issue a warning, or maybe ignore it or raise an exception.");
 
Index: Include/warnings.h
===================================================================
--- Include/warnings.h	(revision 62464)
+++ Include/warnings.h	(working copy)
@@ -9,6 +9,7 @@
 PyAPI_FUNC(int) PyErr_WarnEx(PyObject *, const char *, Py_ssize_t);
 PyAPI_FUNC(int) PyErr_WarnExplicit(PyObject *, const char *, const char *, int,
                                     const char *, PyObject *);
+PyAPI_FUNC(int) PyErr_WarnPy3k(const char *, Py_ssize_t);
 
 /* DEPRECATED: Use PyErr_WarnEx() instead. */
 #define PyErr_Warn(category, msg) PyErr_WarnEx(category, msg, 1)