Index: Doc/lib/libweakref.tex
===================================================================
RCS file: /cvsroot/python/python/dist/src/Doc/lib/libweakref.tex,v
retrieving revision 1.26
diff -u -d -r1.26 libweakref.tex
--- Doc/lib/libweakref.tex	12 Jun 2004 06:56:44 -0000	1.26
+++ Doc/lib/libweakref.tex	2 Jul 2004 16:05:42 -0000
@@ -68,7 +68,7 @@
 information.
 
 
-\begin{funcdesc}{ref}{object\optional{, callback}}
+\begin{classdesc}{ref}{object\optional{, callback}}
 Return a weak reference to \var{object}. The original object can be
 retrieved by calling the reference object if the referent is still
 alive; if the referent is no longer alive, calling the reference
@@ -100,7 +100,11 @@
 \var{callback}). If either referent has been deleted, the
 references are equal only if the reference objects are the same
 object.
-\end{funcdesc}
+
+ \versionchanged[This is now a subclassable type rather than a
+ factory function; it derives from \class{object}]
+ {2.4}
+\end{classdesc}
 
 \begin{funcdesc}{proxy}{object\optional{, callback}}
 Return a proxy to \var{object} which uses a weak reference. This
@@ -236,6 +240,41 @@
 idiom shown above is safe in threaded applications as well as
 single-threaded applications.
 
+Specialized versions of \class{ref} objects can be created through
+subclassing. This is used in the implementation of the
+\class{WeakValueDictionary} to reduce the memory overhead for each
+entry in the mapping. This may be most useful to associate additional
+information with a reference, but could also be used to insert
+additional processing on calls to retrieve the referent.
+
+This example shows how a subclass of \class{ref} can be used to store
+additional information about an object and affect the value that's
+returned when the referent is accessed:
+
+\begin{verbatim}
+import weakref
+
+class ExtendedRef(weakref.ref):
+ def __new__(cls, ob, callback=None, **annotations):
+ weakref.ref.__new__(cls, ob, callback)
+ self.__counter = 0
+
+ def __init__(self, ob, callback=None, **annotations):
+ super(ExtendedRef, self).__init__(ob, callback)
+ for k, v in annotations:
+ setattr(self, k, v)
+
+ def __call__(self):
+ """Return a pair containing the referent and the number of
+ times the reference has been called.
+ """
+ ob = super(ExtendedRef, self)()
+ if ob is not None:
+ self.__counter += 1
+ ob = (ob, self.__counter)
+ return ob
+\end{verbatim}
+
 
 \subsection{Example \label{weakref-example}}
 
 	 	 
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