Raymond Hettinger  committed 74551c0

Document how to change OrderedDict update order from first to last.

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File Doc/library/collections.rst

 are deleted.  But when new keys are added, the keys are appended
 to the end and the sort is not maintained.
+It is also straight-forward to create an ordered dictionary variant
+that the remembers the order the keys were *last* inserted.
+If a new entry overwrites an existing entry, the
+original insertion position is changed and moved to the end::
+    class LastUpdatedOrderedDict(OrderedDict):
+        'Store items is the order the keys were last added'
+        def __setitem__(self, key, value):
+            if key in self:
+                del self[key]
+            OrderedDict.__setitem__(self, key, value)
 :class:`UserDict` objects