- Patch 1433928:

- The copy module now "copies" function objects (as atomic objects).
  - dict.__getitem__ now looks for a __missing__ hook before raising
    KeyError.
  - Added a new type, defaultdict, to the collections module.
    This uses the new __missing__ hook behavior added to dict (see above).

Doc/lib/libcollections.tex

@@ -8,9 +8,10 @@
 \versionadded{2.4}
 
 
-This module implements high-performance container datatypes.  Currently, the
-only datatype is a deque.  Future additions may include B-trees
-and Fibonacci heaps.
+This module implements high-performance container datatypes.  Currently,
+there are two datatypes, deque and defaultdict.
+Future additions may include B-trees and Fibonacci heaps.
+\versionchanged[Added defaultdict]{2.5}
 
 \begin{funcdesc}{deque}{\optional{iterable}}
   Returns a new deque objected initialized left-to-right (using
@@ -211,3 +212,46 @@ def maketree(iterable):
 [[[['a', 'b'], ['c', 'd']], [['e', 'f'], ['g', 'h']]]]
 
 \end{verbatim}
+
+
+
+\begin{funcdesc}{defaultdict}{\optional{default_factory\optional{, ...}}}
+  Returns a new dictionary-like object.  \class{defaultdict} is a subclass
+  of the builtin \class{dict} class.  It overrides one method and adds one
+  writable instance variable.  The remaining functionality is the same as
+  for the \class{dict} class and is not documented here.
+
+  The first argument provides the initial value for the
+  \member{default_factory} attribute; it defaults to \code{None}.
+  All remaining arguments are treated the same as if they were
+  passed to the \class{dict} constructor, including keyword arguments.
+
+ \versionadded{2.5}
+\end{funcdesc}
+
+\class{defaultdict} objects support the following method in addition to
+the standard \class{dict} operations:
+
+\begin{methoddesc}{__missing__}{key}
+  If the \member{default_factory} attribute is \code{None}, this raises
+  an \exception{KeyError} exception with the \var{key} as argument.
+
+  If \member{default_factory} is not \code{None}, it is called without
+  arguments to provide a default value for the given \var{key}, this
+  value is inserted in the dictionary for the \var{key}, and returned.
+
+  If calling \member{default_factory} raises an exception this exception
+  is propagated unchanged.
+
+  This method is called by the \method{__getitem__} method of the
+  \class{dict} class when the requested key is not found; whatever it
+  returns or raises is then returned or raised by \method{__getitem__}.
+\end{methoddesc}
+
+\class{defaultdict} objects support the following instance variable:
+
+\begin{datadesc}{default_factory}
+  This attribute is used by the \method{__missing__} method; it is initialized
+  from the first argument to the constructor, if present, or to \code{None}, 
+  if absent.
+\end{datadesc}

Doc/lib/libcopy.tex

@@ -67,9 +67,12 @@ set of components copied.
 
 \end{itemize}
 
-This version does not copy types like module, class, function, method,
+This module does not copy types like module, method,
 stack trace, stack frame, file, socket, window, array, or any similar
-types.
+types.  It does ``copy'' functions and classes (shallow and deeply),
+by returning the original object unchanged; this is compatible with
+the way these are treated by the \module{pickle} module.
+\versionchanged[Added copying functions]{2.5}
 
 Classes can use the same interfaces to control copying that they use
 to control pickling.  See the description of module

Doc/lib/libstdtypes.tex

@@ -1350,7 +1350,7 @@ arbitrary objects):
 
 \begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes}
   \lineiii{len(\var{a})}{the number of items in \var{a}}{}
-  \lineiii{\var{a}[\var{k}]}{the item of \var{a} with key \var{k}}{(1)}
+  \lineiii{\var{a}[\var{k}]}{the item of \var{a} with key \var{k}}{(1), (10)}
   \lineiii{\var{a}[\var{k}] = \var{v}}
           {set \code{\var{a}[\var{k}]} to \var{v}}
           {}
@@ -1454,6 +1454,17 @@ then is updated with those key/value pairs:
 \versionchanged[Allowed the argument to be an iterable of key/value
                 pairs and allowed keyword arguments]{2.4}
 
+\item[(10)] If a subclass of dict defines a method \method{__missing__},
+if the key \var{k} is not present, the \var{a}[\var{k}] operation calls
+that method with the key \var{k} as argument.  The \var{a}[\var{k}]
+operation then returns or raises whatever is returned or raised by the
+\function{__missing__}(\var{k}) call if the key is not present.
+No other operations or methods invoke \method{__missing__}().
+If \method{__missing__} is not defined, \exception{KeyError} is raised.
+\method{__missing__} must be a method; it cannot be an instance variable.
+For an example, see \module{collections}.\class{defaultdict}.
+\versionadded{2.5}
+
 \end{description}
 
 \subsection{File Objects