Index: library/collections.rst
===================================================================
--- library/collections.rst	(revision 83761)
+++ library/collections.rst	(working copy)
@@ -557,49 +557,48 @@
 
 .. class:: defaultdict([default_factory[, ...]])
 
-   Returns a new dictionary-like object.  :class:`defaultdict` is a subclass of the
-   built-in :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.
+   :class:`defaultdict` is a :class:`dict` subclass that can guarantee
+   success on key lookups: if a key does not currently exist in a
+   ``defaultdict`` object, a "default value factory" is called to
+   provide a value for that key.  The "default value factory" is
+   a callable object (typically, a function) that takes no
+   arguments. You specify this callable as the first argument to
+   ``defaultdict()``; additional arguments are the
+   same as for :class:`dict()`.
+   
+   The "default value factory" callable is stored as an
+   attribute, :attr:`default_factory`, of the newly created defaultdict
+   object. If you call ``defaultdict()`` with no arguments, or with
+   ``None`` as the first argument, the :attr:`default_factory` attribute is
+   set to ``None``. You can reassign the :attr:`default_factory` attribute
+   of an existing ``defaultdict`` object to another callable, or to
+   ``None``.
+   
+   When a lookup of a non-existent key is performed in a
+   ``defaultdict`` object, its :attr:`default_factory` attribute is
+   evaluated, and the resulting object is called (unless it
+   is ``None``):
+   
+   * If the call produces a value, that value is returned as the
+     result of the lookup. In addition, the key-value pair is
+     inserted into the ``defaultdict``.
 
-   The first argument provides the initial value for the :attr:`default_factory`
-   attribute; it defaults to ``None``. All remaining arguments are treated the same
-   as if they were passed to the :class:`dict` constructor, including keyword
-   arguments.
+   * If the call raises an exception, the exception is propagated 
+     unchanged.
 
+   * If the :attr:`default_factory` attribute evaluates to 
+     ``None``, a :exc:`KeyError` exception is raised, with the 
+     non-existent key as its argument. (The ``defaultdict`` behaves 
+     exactly like a standard :class:`dict` in this case.)
+     
    .. versionadded:: 2.5
 
-   :class:`defaultdict` objects support the following method in addition to the
-   standard :class:`dict` operations:
+   If the ``defaultdict`` class does not provide exactly the 
+   functionality you need, consider creating your own subclass of 
+   :class:`dict` that implements the special method 
+   :meth:`__missing__`. See the description of the :class:`dict`
+   class's "d[key]" operation for details.
 
-
-   .. method:: defaultdict.__missing__(key)
-
-      If the :attr:`default_factory` attribute is ``None``, this raises a
-      :exc:`KeyError` exception with the *key* as argument.
-
-      If :attr:`default_factory` is not ``None``, it is called without arguments
-      to provide a default value for the given *key*, this value is inserted in
-      the dictionary for the *key*, and returned.
-
-      If calling :attr:`default_factory` raises an exception this exception is
-      propagated unchanged.
-
-      This method is called by the :meth:`__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 :meth:`__getitem__`.
-
-
-   :class:`defaultdict` objects support the following instance variable:
-
-
-   .. attribute:: defaultdict.default_factory
-
-      This attribute is used by the :meth:`__missing__` method; it is
-      initialized from the first argument to the constructor, if present, or to
-      ``None``, if absent.
-
-
 :class:`defaultdict` Examples
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^