Index: release25-maint/Lib/_threading_local.py
===================================================================
--- release25-maint/Lib/_threading_local.py	(revision 60064)
+++ release25-maint/Lib/_threading_local.py	(working copy)
@@ -130,6 +130,26 @@
   >>> mydata.number
   11
 
+Attributes on a local are cleaned up when the assigning thread finishes:
+
+    >>> import weakref
+    >>> mydata = threading.local()
+
+    >>> class SomeObj(object):
+    ...     instances=weakref.WeakValueDictionary()
+    ...     def __init__(self):
+    ...         self.instances[id(self)]=self
+        
+    >>> def doit():
+    ...     mydata.x=SomeObj()
+    
+    >>> t=threading.Thread(target=doit)
+    >>> t.start()
+    >>> t.join()
+    >>> del t
+    >>> SomeObj.instances.values()
+    []
+
 >>> del mydata
 """