diff -r be663c9a9e24 Include/abstract.h
--- a/Include/abstract.h	Thu Feb 09 23:49:50 2017 +0100
+++ b/Include/abstract.h	Fri Feb 10 08:23:50 2017 +0900
@@ -311,6 +311,10 @@ PyAPI_FUNC(PyObject *) PyObject_CallMeth
 PyAPI_FUNC(PyObject *) _PyObject_CallMethodId(PyObject *obj,
                                               _Py_Identifier *name,
                                               const char *format, ...);
+
+/* Like PyObject_GenericGetAttr(), but may return unbound instance method. */
+PyAPI_FUNC(int) _PyObject_GetMethod(PyObject *obj, PyObject *name,
+                                    PyObject **method);
 #endif /* !Py_LIMITED_API */
 
 PyAPI_FUNC(PyObject *) _PyObject_CallFunction_SizeT(PyObject *callable,
diff -r be663c9a9e24 Objects/abstract.c
--- a/Objects/abstract.c	Thu Feb 09 23:49:50 2017 +0100
+++ b/Objects/abstract.c	Fri Feb 10 08:23:50 2017 +0900
@@ -2616,10 +2616,10 @@ static PyObject *
     }
 
     if (is_size_t) {
-        stack = _Py_VaBuildStack(small_stack, small_stack_len, format, va, &nargs);
+        stack = _Py_VaBuildStack_SizeT(small_stack, small_stack_len, format, va, &nargs);
     }
     else {
-        stack = _Py_VaBuildStack_SizeT(small_stack, small_stack_len, format, va, &nargs);
+        stack = _Py_VaBuildStack(small_stack, small_stack_len, format, va, &nargs);
     }
     if (stack == NULL) {
         return NULL;
@@ -2687,6 +2687,32 @@ callmethod(PyObject* callable, const cha
     return _PyObject_CallFunctionVa(callable, format, va, is_size_t);
 }
 
+// Helper function for PyObject_CallMetho[Id]() when no arguments.
+// try to skip temporal method object and argument allocation.
+static PyObject*
+callmethod_noarg(PyObject *obj, PyObject *name)
+{
+    if (!name) {  // caller can pass _PyUnicode_FromId() directly
+        return NULL;
+    }
+
+    PyObject *callable = NULL, *retval;
+    int unbound = _PyObject_GetMethod(obj, name, &callable);
+    if (callable == NULL) {
+        return NULL;
+    }
+
+    if (unbound) {
+        retval = _PyObject_FastCall(callable, &obj, 1);
+    }
+    else {
+        retval = _PyObject_CallNoArg(callable);
+    }
+
+    Py_DECREF(callable);
+    return retval;
+}
+
 PyObject *
 PyObject_CallMethod(PyObject *obj, const char *name, const char *format, ...)
 {
@@ -2697,6 +2723,13 @@ PyObject_CallMethod(PyObject *obj, const
         return null_error();
     }
 
+    if (!format || !*format) {
+        PyObject *nameobj = PyUnicode_FromString(name);
+        retval = callmethod_noarg(obj, nameobj);
+        Py_XDECREF(nameobj);
+        return retval;
+    }
+
     callable = PyObject_GetAttrString(obj, name);
     if (callable == NULL)
         return NULL;
@@ -2720,6 +2753,10 @@ PyObject *
         return null_error();
     }
 
+    if (!format || !*format) {
+        return callmethod_noarg(obj, _PyUnicode_FromId(name));
+    }
+
     callable = _PyObject_GetAttrId(obj, name);
     if (callable == NULL)
         return NULL;
@@ -2743,6 +2780,13 @@ PyObject *
         return null_error();
     }
 
+    if (!format || !*format) {
+        PyObject *nameobj = PyUnicode_FromString(name);
+        retval = callmethod_noarg(obj, nameobj);
+        Py_XDECREF(nameobj);
+        return retval;
+    }
+
     callable = PyObject_GetAttrString(obj, name);
     if (callable == NULL)
         return NULL;
@@ -2766,6 +2810,10 @@ PyObject *
         return null_error();
     }
 
+    if (!format || !*format) {
+        return callmethod_noarg(obj, _PyUnicode_FromId(name));
+    }
+
     callable = _PyObject_GetAttrId(obj, name);
     if (callable == NULL) {
         return NULL;
@@ -2780,13 +2828,12 @@ PyObject *
 }
 
 static PyObject *
-object_vacall(PyObject *callable, va_list vargs)
+object_vacall(PyObject *callable, PyObject *self, va_list vargs)
 {
     PyObject *small_stack[_PY_FASTCALL_SMALL_STACK];
     PyObject **stack;
     Py_ssize_t nargs;
     PyObject *result;
-    Py_ssize_t i;
     va_list countva;
 
     if (callable == NULL) {
@@ -2795,7 +2842,7 @@ object_vacall(PyObject *callable, va_lis
 
     /* Count the number of arguments */
     va_copy(countva, vargs);
-    nargs = 0;
+    nargs = (self != NULL);
     while (1) {
         PyObject *arg = va_arg(countva, PyObject *);
         if (arg == NULL) {
@@ -2817,7 +2864,11 @@ object_vacall(PyObject *callable, va_lis
         }
     }
 
-    for (i = 0; i < nargs; ++i) {
+    Py_ssize_t i = 0;
+    if (self != NULL) {
+        stack[i++] = self;
+    }
+    for (; i < nargs; ++i) {
         stack[i] = va_arg(vargs, PyObject *);
     }
 
@@ -2831,22 +2882,23 @@ object_vacall(PyObject *callable, va_lis
 }
 
 PyObject *
-PyObject_CallMethodObjArgs(PyObject *callable, PyObject *name, ...)
+PyObject_CallMethodObjArgs(PyObject *obj, PyObject *name, ...)
 {
     va_list vargs;
     PyObject *result;
 
-    if (callable == NULL || name == NULL) {
+    if (obj == NULL || name == NULL) {
         return null_error();
     }
 
-    callable = PyObject_GetAttr(callable, name);
+    PyObject *callable = NULL;
+    int unbound = _PyObject_GetMethod(obj, name, &callable);
     if (callable == NULL) {
         return NULL;
     }
 
     va_start(vargs, name);
-    result = object_vacall(callable, vargs);
+    result = object_vacall(callable, unbound ? obj : NULL, vargs);
     va_end(vargs);
 
     Py_DECREF(callable);
@@ -2858,19 +2910,23 @@ PyObject *
                               struct _Py_Identifier *name, ...)
 {
     va_list vargs;
-    PyObject *callable, *result;
+    PyObject *callable = NULL, *result;
 
     if (obj == NULL || name == NULL) {
         return null_error();
     }
 
-    callable = _PyObject_GetAttrId(obj, name);
+    PyObject *nameobj = _PyUnicode_FromId(name);  // borrowed
+    if (nameobj == NULL) {
+        return NULL;
+    }
+    int unbound = _PyObject_GetMethod( obj, nameobj, &callable);
     if (callable == NULL) {
         return NULL;
     }
 
     va_start(vargs, name);
-    result = object_vacall(callable, vargs);
+    result = object_vacall(callable, unbound ? obj : NULL, vargs);
     va_end(vargs);
 
     Py_DECREF(callable);
@@ -2884,7 +2940,7 @@ PyObject_CallFunctionObjArgs(PyObject *c
     PyObject *result;
 
     va_start(vargs, callable);
-    result = object_vacall(callable, vargs);
+    result = object_vacall(callable, NULL, vargs);
     va_end(vargs);
 
     return result;
diff -r be663c9a9e24 Python/ceval.c
--- a/Python/ceval.c	Thu Feb 09 23:49:50 2017 +0100
+++ b/Python/ceval.c	Fri Feb 10 08:23:50 2017 +0900
@@ -30,9 +30,6 @@
 #define CHECKEXC 1      /* Double-check exception checking */
 #endif
 
-/* Private API for the LOAD_METHOD opcode. */
-extern int _PyObject_GetMethod(PyObject *, PyObject *, PyObject **);
-
 typedef PyObject *(*callproc)(PyObject *, PyObject *, PyObject *);
 
 /* Forward declarations */