diff -r 817a003ecdc6 Include/unicodeobject.h
--- a/Include/unicodeobject.h	Sun Nov 13 23:36:30 2016 +0000
+++ b/Include/unicodeobject.h	Mon Nov 14 13:20:02 2016 +0800
@@ -2037,7 +2037,7 @@
     );
 
 #ifndef Py_LIMITED_API
-PyAPI_FUNC(int) _PyUnicode_CompareWithId(
+PyAPI_FUNC(int) _PyUnicode_EqualToId(
     PyObject *left,             /* Left string */
     _Py_Identifier *right       /* Right identifier */
     );
diff -r 817a003ecdc6 Objects/typeobject.c
--- a/Objects/typeobject.c	Sun Nov 13 23:36:30 2016 +0000
+++ b/Objects/typeobject.c	Mon Nov 14 13:20:02 2016 +0800
@@ -863,7 +863,7 @@
         return NULL;
     }
 
-    if (mod != NULL && _PyUnicode_CompareWithId(mod, &PyId_builtins))
+    if (mod != NULL && !_PyUnicode_EqualToId(mod, &PyId_builtins))
         rtn = PyUnicode_FromFormat("<class '%U.%U'>", mod, name);
     else
         rtn = PyUnicode_FromFormat("<class '%s'>", type->tp_name);
@@ -2403,7 +2403,7 @@
             if (!valid_identifier(tmp))
                 goto error;
             assert(PyUnicode_Check(tmp));
-            if (_PyUnicode_CompareWithId(tmp, &PyId___dict__) == 0) {
+            if (_PyUnicode_EqualToId(tmp, &PyId___dict__)) {
                 if (!may_add_dict || add_dict) {
                     PyErr_SetString(PyExc_TypeError,
                         "__dict__ slot disallowed: "
@@ -2434,7 +2434,7 @@
         for (i = j = 0; i < nslots; i++) {
             tmp = PyTuple_GET_ITEM(slots, i);
             if ((add_dict &&
-                 _PyUnicode_CompareWithId(tmp, &PyId___dict__) == 0) ||
+                 _PyUnicode_EqualToId(tmp, &PyId___dict__)) ||
                 (add_weak &&
                  PyUnicode_CompareWithASCIIString(tmp, "__weakref__") == 0))
                 continue;
@@ -3538,11 +3538,10 @@
         Py_XDECREF(mod);
         return NULL;
     }
-    if (mod != NULL && _PyUnicode_CompareWithId(mod, &PyId_builtins))
+    if (mod != NULL && !_PyUnicode_EqualToId(mod, &PyId_builtins))
         rtn = PyUnicode_FromFormat("<%U.%U object at %p>", mod, name, self);
     else
-        rtn = PyUnicode_FromFormat("<%s object at %p>",
-                                  type->tp_name, self);
+        rtn = PyUnicode_FromFormat("<%s object at %p>", type->tp_name, self);
     Py_XDECREF(mod);
     Py_DECREF(name);
     return rtn;
@@ -7238,7 +7237,7 @@
        (i.e. super, or a subclass), not the class of su->obj. */
     if (PyUnicode_Check(name) &&
         PyUnicode_GET_LENGTH(name) == 9 &&
-        _PyUnicode_CompareWithId(name, &PyId___class__) == 0)
+        _PyUnicode_EqualToId(name, &PyId___class__))
         goto skip;
 
     mro = starttype->tp_mro;
@@ -7450,7 +7449,7 @@
         for (i = 0; i < n; i++) {
             PyObject *name = PyTuple_GET_ITEM(co->co_freevars, i);
             assert(PyUnicode_Check(name));
-            if (!_PyUnicode_CompareWithId(name, &PyId___class__)) {
+            if (_PyUnicode_EqualToId(name, &PyId___class__)) {
                 Py_ssize_t index = co->co_nlocals +
                     PyTuple_GET_SIZE(co->co_cellvars) + i;
                 PyObject *cell = f->f_localsplus[index];
diff -r 817a003ecdc6 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Sun Nov 13 23:36:30 2016 +0000
+++ b/Objects/unicodeobject.c	Mon Nov 14 13:20:02 2016 +0800
@@ -10992,13 +10992,32 @@
     return -1;
 }
 
+/* Test whether a unicode is equal to an identifier. Return 1 if true
+   otherwise 0. Any error occurs inside is treated as not equal and
+   will be cleared before return. */
 int
-_PyUnicode_CompareWithId(PyObject *left, _Py_Identifier *right)
-{
-    PyObject *right_str = _PyUnicode_FromId(right);   /* borrowed */
-    if (right_str == NULL)
-        return -1;
-    return PyUnicode_Compare(left, right_str);
+_PyUnicode_EqualToId(PyObject *left, _Py_Identifier *right)
+{
+    if (!PyUnicode_Check(left)) {
+        return 0;
+    }
+
+    if (PyUnicode_READY(left) == -1) {
+        PyErr_Clear();
+        return 0;
+    }
+
+    PyObject *right_uni = _PyUnicode_FromId(right);   /* borrowed */
+    if (right_uni == NULL) {
+        PyErr_Clear();
+        return (PyUnicode_CompareWithASCIIString(left, right->string) == 0);
+    }
+
+    if (left == right_uni) {
+        return 1;
+    }
+
+    return unicode_compare_eq(left, right_uni);
 }
 
 int
diff -r 817a003ecdc6 Python/errors.c
--- a/Python/errors.c	Sun Nov 13 23:36:30 2016 +0000
+++ b/Python/errors.c	Mon Nov 14 13:20:02 2016 +0800
@@ -984,7 +984,7 @@
             goto done;
     }
     else {
-        if (_PyUnicode_CompareWithId(moduleName, &PyId_builtins) != 0) {
+        if (!_PyUnicode_EqualToId(moduleName, &PyId_builtins)) {
             if (PyFile_WriteObject(moduleName, f, Py_PRINT_RAW) < 0)
                 goto done;
             if (PyFile_WriteString(".", f) < 0)
diff -r 817a003ecdc6 Python/pythonrun.c
--- a/Python/pythonrun.c	Sun Nov 13 23:36:30 2016 +0000
+++ b/Python/pythonrun.c	Mon Nov 14 13:20:02 2016 +0800
@@ -751,7 +751,7 @@
             err = PyFile_WriteString("<unknown>", f);
         }
         else {
-            if (_PyUnicode_CompareWithId(moduleName, &PyId_builtins) != 0)
+            if (!_PyUnicode_EqualToId(moduleName, &PyId_builtins))
             {
                 err = PyFile_WriteObject(moduleName, f, Py_PRINT_RAW);
                 err += PyFile_WriteString(".", f);