diff -r bb7363b8b50e Doc/library/datetime.rst
--- a/Doc/library/datetime.rst	Fri Sep 11 11:31:07 2015 -0700
+++ b/Doc/library/datetime.rst	Mon Oct 05 00:50:51 2015 +0530
@@ -1872,6 +1872,14 @@
 |           | or -HHMM (empty string if the  | +1030                  |       |
 |           | the object is naive).          |                        |       |
 +-----------+--------------------------------+------------------------+-------+
+| ``%:z``   | UTC offset in the form +HH:MM  | (empty), +00:00,       |       |
+|           | or -HH:MM (empty string if the | -04:00, +10:30         |       |
+|           | the object is naive).          |                        |       |
++-----------+--------------------------------+------------------------+-------+
+| ``%::z``  | UTC offset in the form         | (empty), +00:00:00,    |       |
+|           | +HH:MM:SS or -HH:MM:SS (empty  | -04:00:20, +10:30:37   |       |
+|           | string if the object is naive).|                        |       |
++-----------+--------------------------------+------------------------+-------+
 | ``%Z``    | Time zone name (empty string   | (empty), UTC, EST, CST |       |
 |           | if the object is naive).       |                        |       |
 +-----------+--------------------------------+------------------------+-------+
diff -r bb7363b8b50e Modules/_datetimemodule.c
--- a/Modules/_datetimemodule.c	Fri Sep 11 11:31:07 2015 -0700
+++ b/Modules/_datetimemodule.c	Mon Oct 05 00:50:51 2015 +0530
@@ -1039,7 +1039,7 @@
  */
 static int
 format_utcoffset(char *buf, size_t buflen, const char *sep,
-                PyObject *tzinfo, PyObject *tzinfoarg)
+                PyObject *tzinfo, PyObject *tzinfoarg, PyObject *secondsrequired)
 {
     PyObject *offset;
     int hours, minutes, seconds;
@@ -1072,9 +1072,14 @@
     Py_DECREF(offset);
     minutes = divmod(seconds, 60, &seconds);
     hours = divmod(minutes, 60, &minutes);
-    assert(seconds == 0);
+    /* assert(seconds == 0) */
     /* XXX ignore sub-minute data, curently not allowed. */
+    if ((PyObject *)secondsrequired == Py_True){
+    PyOS_snprintf(buf, buflen, "%c%02d%s%02d%s%02d", sign, hours, sep, minutes, sep, seconds);
+    }
+    else{
     PyOS_snprintf(buf, buflen, "%c%02d%s%02d", sign, hours, sep, minutes);
+    }
 
     return 0;
 }
@@ -1201,6 +1206,45 @@
             goto Done;
         }
         /* A % has been seen and ch is the character after it. */
+        else if (ch == ':') {
+                 if (zreplacement == NULL) {
+                /* format utcoffset */
+                char buf[100];
+                PyObject *tzinfo = get_tzinfo_member(object);
+                zreplacement = PyBytes_FromStringAndSize("", 0);
+                if (zreplacement == NULL) goto Done;
+                if (tzinfo != Py_None && tzinfo != NULL) {
+                    assert(tzinfoarg != NULL);
+                    /* If the next character after ':' is 'z' return the timzone formatted as signHH:MM */
+                    if ((ch = *pin++) == 'z') {
+                    if (format_utcoffset(buf,
+                                         sizeof(buf),
+                                         ":",
+                                         tzinfo,
+                                         tzinfoarg, Py_False) < 0)
+                        goto Done;
+                    }
+                    if (ch == ':' && (ch == *pin++)!='\0' && ch == 'z'){
+                    if (format_utcoffset(buf,
+                                         sizeof(buf),
+                                         ":",
+                                         tzinfo,
+                                         tzinfoarg, Py_True) < 0)
+                        goto Done;
+                                         
+                    }
+                    Py_DECREF(zreplacement);
+                    zreplacement =
+                      PyBytes_FromStringAndSize(buf,
+                                               strlen(buf));
+                    if (zreplacement == NULL)
+                        goto Done;
+                }
+            }
+            assert(zreplacement != NULL);
+            ptoappend = PyBytes_AS_STRING(zreplacement);
+            ntoappend = PyBytes_GET_SIZE(zreplacement);
+        }
         else if (ch == 'z') {
             if (zreplacement == NULL) {
                 /* format utcoffset */
@@ -1214,7 +1258,7 @@
                                          sizeof(buf),
                                          "",
                                          tzinfo,
-                                         tzinfoarg) < 0)
+                                         tzinfoarg, Py_False) < 0)
                         goto Done;
                     Py_DECREF(zreplacement);
                     zreplacement =
@@ -3635,7 +3679,7 @@
 
     /* We need to append the UTC offset. */
     if (format_utcoffset(buf, sizeof(buf), ":", self->tzinfo,
-                         Py_None) < 0) {
+                         Py_None, Py_False) < 0) {
         Py_DECREF(result);
         return NULL;
     }
@@ -4512,7 +4556,7 @@
 
     /* We need to append the UTC offset. */
     if (format_utcoffset(buffer, sizeof(buffer), ":", self->tzinfo,
-                         (PyObject *)self) < 0) {
+                         (PyObject *)self, Py_False) < 0) {
         Py_DECREF(result);
         return NULL;
     }