Index: Objects/unicodeobject.c
===================================================================
--- Objects/unicodeobject.c	(wersja 79046)
+++ Objects/unicodeobject.c	(kopia robocza)
@@ -8666,6 +8666,7 @@
     {"isprintable", (PyCFunction) unicode_isprintable, METH_NOARGS, isprintable__doc__},
     {"zfill", (PyCFunction) unicode_zfill, METH_VARARGS, zfill__doc__},
     {"format", (PyCFunction) do_string_format, METH_VARARGS | METH_KEYWORDS, format__doc__},
+    {"format_using_mapping", (PyCFunction) do_string_format_using_mapping, METH_O, format__doc__},
     {"__format__", (PyCFunction) unicode__format__, METH_VARARGS, p_format__doc__},
     {"_formatter_field_name_split", (PyCFunction) formatter_field_name_split, METH_NOARGS},
     {"_formatter_parser", (PyCFunction) formatter_parser, METH_NOARGS},
Index: Objects/stringlib/string_format.h
===================================================================
--- Objects/stringlib/string_format.h	(wersja 79046)
+++ Objects/stringlib/string_format.h	(kopia robocza)
@@ -496,9 +496,21 @@
         if (key == NULL)
             goto error;
         if ((kwargs == NULL) || (obj = PyDict_GetItem(kwargs, key)) == NULL) {
-            PyErr_SetObject(PyExc_KeyError, key);
-            Py_DECREF(key);
-            goto error;
+            PyObject *missing;
+            static PyObject *missing_str = NULL;
+            missing = _PyObject_LookupSpecial((PyObject *) kwargs,
+                                              "__missing__",
+                                              &missing_str);
+            if (missing != NULL) {
+                obj = PyObject_CallFunctionObjArgs(missing, key, NULL);
+                Py_DECREF(missing);
+            }
+            else {            
+                PyErr_SetObject(PyExc_KeyError, key);
+				Py_DECREF(missing);
+                Py_DECREF(key);
+                goto error;
+            }
         }
         Py_DECREF(key);
         Py_INCREF(obj);
@@ -1035,6 +1047,11 @@
     return build_string(&input, args, kwargs, recursion_depth, &auto_number);
 }
 
+static PyObject *
+do_string_format_using_mapping(PyObject *self, PyObject *obj)
+{
+    return do_string_format(self, NULL, obj);
+}
 
 
 /************************************************************************/