Index: py3k/Doc/library/datetime.rst
===================================================================
--- py3k/Doc/library/datetime.rst	(revision 81033)
+++ py3k/Doc/library/datetime.rst	(working copy)
@@ -1003,6 +1003,21 @@
       '2002-12-25 00:00:00-06:39'
 
 
+.. method:: datetime.rfcformat(default_utcoffset='-00:00')
+
+   Return a string representing the date and time in RFC 3339 format,
+   YYYY-MM-DDTHH:MM:SS.mmmmmm+HH:MM or, if :attr:`microsecond` is 0,
+   YYYY-MM-DDTHH:MM:SS+HH:MM
+
+   This method differs from :meth:`isoformat` in that the separator is
+   always 'T', and the string always contains the UTC offset.  For
+   naive instances the default UTC offset is *default_utcoffset*.
+   For example,
+
+      >>> datetime(2010, 4, 12).rfcformat()
+      '2010-04-12T00:00:00-00:00'
+
+
 .. method:: datetime.__str__()
 
    For a :class:`datetime` instance *d*, ``str(d)`` is equivalent to
Index: py3k/Lib/test/test_datetime.py
===================================================================
--- py3k/Lib/test/test_datetime.py	(revision 81033)
+++ py3k/Lib/test/test_datetime.py	(working copy)
@@ -1243,6 +1243,34 @@
         # str is ISO format with the separator forced to a blank.
         self.assertEqual(str(t), "0002-03-02 00:00:00")
 
+    def test_rfcformat(self):
+        t = self.theclass(2, 3, 2, 4, 5, 1, 123)
+        self.assertEqual(t.rfcformat(), "0002-03-02T04:05:01.000123-00:00")
+
+        t = self.theclass(2, 3, 2, 4, 5, 1, 0)
+        self.assertEqual(t.rfcformat(), "0002-03-02T04:05:01-00:00")
+
+        t = self.theclass(2, 3, 2)
+        self.assertEqual(t.rfcformat(), "0002-03-02T00:00:00-00:00")
+
+        # with default UTC offset argument:
+        self.assertEqual(t.rfcformat("Z"), "0002-03-02T00:00:00Z")
+        self.assertEqual(t.rfcformat("+00:00"), "0002-03-02T00:00:00+00:00")
+        self.assertEqual(t.rfcformat(default_utcoffset="Z"),
+                         "0002-03-02T00:00:00Z")
+        self.assertEqual(t.rfcformat(default_utcoffset="+00:00"),
+                         "0002-03-02T00:00:00+00:00")
+
+        # with tzinfo:
+        t = self.theclass(2, 3, 2, 4, 5, 1, 123, FixedOffset(0, "UTC"))
+        self.assertEqual(t.rfcformat(), "0002-03-02T04:05:01.000123+00:00")
+
+        t = self.theclass(2, 3, 2, 4, 5, 1, 123, FixedOffset(77, "77min"))
+        self.assertEqual(t.rfcformat(), "0002-03-02T04:05:01.000123+01:17")
+
+        # with default UTC offset argument (shouldn't use the default):
+        self.assertEqual(t.rfcformat("Z"), "0002-03-02T04:05:01.000123+01:17")
+
     def test_format(self):
         dt = self.theclass(2007, 9, 10, 4, 5, 1, 123)
         self.assertEqual(dt.__format__(''), str(dt))
Index: py3k/Modules/datetimemodule.c
===================================================================
--- py3k/Modules/datetimemodule.c	(revision 81033)
+++ py3k/Modules/datetimemodule.c	(working copy)
@@ -4342,6 +4342,58 @@
 }
 
 static PyObject *
+datetime_rfcformat(PyDateTime_DateTime *self, PyObject *args, PyObject *kw)
+{
+    char buffer[100];
+    PyObject *result;
+    int us = DATE_GET_MICROSECOND(self);
+    PyObject *utcoffset = NULL;
+    static char *keywords[] = {"default_utcoffset", NULL};
+
+    if (!PyArg_ParseTupleAndKeywords(args, kw, "|U:rfcformat", keywords,
+                                     &utcoffset))
+        return NULL;
+
+    /* If we know the UTC offset, set to that: */
+    if (HASTZINFO(self)) {
+        if (format_utcoffset(buffer, sizeof(buffer), ":", self->tzinfo,
+                             (PyObject *)self) < 0) {
+            return NULL;
+        }
+        else {
+            utcoffset = PyUnicode_FromString(buffer);
+        }
+    }
+    /* Else set to the default: */
+    else {
+        if (utcoffset == NULL) {
+            /* We didn't got the default from the caller, use "-00:00": */
+            utcoffset = PyUnicode_FromString("-00:00");
+        }
+        else {
+            /* We got the default from the caller, use it: */
+            Py_INCREF(utcoffset);
+        }
+    }
+
+    if (us)
+        result = PyUnicode_FromFormat("%04d-%02d-%02dT%02d:%02d:%02d.%06d",
+                                      GET_YEAR(self), GET_MONTH(self),
+                                      GET_DAY(self),
+                                      DATE_GET_HOUR(self), DATE_GET_MINUTE(self),
+                                      DATE_GET_SECOND(self), us);
+    else
+        result = PyUnicode_FromFormat("%04d-%02d-%02dT%02d:%02d:%02d",
+                                      GET_YEAR(self), GET_MONTH(self),
+                                      GET_DAY(self),
+                                      DATE_GET_HOUR(self), DATE_GET_MINUTE(self),
+                                      DATE_GET_SECOND(self));
+
+    PyUnicode_AppendAndDel(&result, utcoffset);
+    return result;
+}
+
+static PyObject *
 datetime_ctime(PyDateTime_DateTime *self)
 {
     return format_ctime((PyDateTime_Date *)self,
@@ -4730,6 +4782,12 @@
                "sep is used to separate the year from the time, and "
                "defaults to 'T'.")},
 
+    {"rfcformat",   (PyCFunction)datetime_rfcformat, METH_VARARGS | METH_KEYWORDS,
+     PyDoc_STR("[default_utcoffset] -> string in RFC 3339 format, "
+               "YYYY-MM-DDTHH:MM:SS[.mmmmmm]+HH:MM.\n\n"
+               "default_utcoffset is used as the UTC offset for naive "
+               "instances, and defaults to '-00:00'.")},
+
     {"utcoffset",       (PyCFunction)datetime_utcoffset, METH_NOARGS,
      PyDoc_STR("Return self.tzinfo.utcoffset(self).")},