bpo-27741: Better wording for datetime.strptime() (GH-9994)

Doc/library/datetime.rst

@@ -2016,7 +2016,9 @@ although not all objects support a :meth:`timetuple` method.
 Conversely, the :meth:`datetime.strptime` class method creates a
 :class:`.datetime` object from a string representing a date and time and a
 corresponding format string. ``datetime.strptime(date_string, format)`` is
-equivalent to ``datetime(*(time.strptime(date_string, format)[0:6]))``.
+equivalent to ``datetime(*(time.strptime(date_string, format)[0:6]))``, except
+when the format includes sub-second components or timezone offset information,
+which are supported in ``datetime.strptime`` but are discarded by ``time.strptime``.
 
 For :class:`.time` objects, the format codes for year, month, and day should not
 be used, as time objects have no such values.  If they're used anyway, ``1900``