Closes Issue#22241: timezone.utc name is now plain 'UTC', not 'UTC-00:00'.

Doc/library/datetime.rst

@@ -1734,10 +1734,7 @@ made to civil time.
   otherwise :exc:`ValueError` is raised.
 
   The *name* argument is optional.  If specified it must be a string that
-  is used as the value returned by the ``tzname(dt)`` method.  Otherwise,
-  ``tzname(dt)`` returns a string 'UTCsHH:MM', where s is the sign of
-  *offset*, HH and MM are two digits of ``offset.hours`` and
-  ``offset.minutes`` respectively.
+  will be used as the value returned by the :meth:`datetime.tzname` method.
 
   .. versionadded:: 3.2
 
@@ -1750,11 +1747,19 @@ made to civil time.
 
 .. method:: timezone.tzname(dt)
 
-  Return the fixed value specified when the :class:`timezone` instance is
-  constructed or a string 'UTCsHH:MM', where s is the sign of
-  *offset*, HH and MM are two digits of ``offset.hours`` and
+  Return the fixed value specified when the :class:`timezone` instance
+  is constructed.  If *name* is not provided in the constructor, the
+  name returned by ``tzname(dt)`` is generated from the value of the
+  ``offset`` as follows.  If *offset* is ``timedelta(0)``, the name
+  is "UTC", otherwise it is a string 'UTC±HH:MM', where ± is the sign
+  of ``offset``, HH and MM are two digits of ``offset.hours`` and
   ``offset.minutes`` respectively.
 
+  .. versionchanged:: 3.6
+  Name generated from ``offset=timedelta(0)`` is now plain 'UTC', not
+  'UTC+00:00'.
+
+
 .. method:: timezone.dst(dt)
 
   Always returns ``None``.

Lib/datetime.py

@@ -1920,6 +1920,8 @@ class timezone(tzinfo):
 
     @staticmethod
     def _name_from_offset(delta):
+        if not delta:
+            return 'UTC'
         if delta < timedelta(0):
             sign = '-'
             delta = -delta

Lib/test/datetimetester.py

@@ -258,7 +258,8 @@ class TestTimeZone(unittest.TestCase):
         with self.assertRaises(TypeError): self.EST.dst(5)
 
     def test_tzname(self):
-        self.assertEqual('UTC+00:00', timezone(ZERO).tzname(None))
+        self.assertEqual('UTC', timezone.utc.tzname(None))
+        self.assertEqual('UTC', timezone(ZERO).tzname(None))
         self.assertEqual('UTC-05:00', timezone(-5 * HOUR).tzname(None))
         self.assertEqual('UTC+09:30', timezone(9.5 * HOUR).tzname(None))
         self.assertEqual('UTC-00:01', timezone(timedelta(minutes=-1)).tzname(None))

Misc/NEWS

@@ -17,6 +17,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #22241: timezone.utc name is now plain 'UTC', not 'UTC-00:00'. 
+
 - Issue #23517: fromtimestamp() and utcfromtimestamp() methods of
   datetime.datetime now round microseconds to nearest with ties going away from
   zero (ROUND_HALF_UP), as Python 2 and Python older than 3.3, instead of

Modules/_datetimemodule.c

@@ -3267,6 +3267,11 @@ timezone_str(PyDateTime_TimeZone *self)
         Py_INCREF(self->name);
         return self->name;
     }
+    if (self == PyDateTime_TimeZone_UTC ||
+           (GET_TD_DAYS(self->offset) == 0 &&
+            GET_TD_SECONDS(self->offset) == 0 &&
+            GET_TD_MICROSECONDS(self->offset) == 0))
+        return PyUnicode_FromString("UTC");
     /* Offset is normalized, so it is negative if days < 0 */
     if (GET_TD_DAYS(self->offset) < 0) {
         sign = '-';