whatsnew: DynanicClassAttribute (#19030), Py_SetStandardStreamEncoding (#16129)

Adding missing docs for DynamicClassAttribute by copying the docstring.  The
doc entry could stand some expansion, which I will note on the issue.

Doc/library/types.rst

@@ -15,6 +15,9 @@ It also defines names for some object types that are used by the standard
 Python interpreter, but not exposed as builtins like :class:`int` or
 :class:`str` are.
 
+Finally, it provides some additional type-related utility classes and functions
+that are not fundamental enough to be builtins.
+
 
 Dynamic Type Creation
 ---------------------
@@ -220,6 +223,9 @@ Standard names are defined for the following types:
       Return a new view of the underlying mapping's values.
 
 
+Additional Utility Classes and Functions
+----------------------------------------
+
 .. class:: SimpleNamespace
 
    A simple :class:`object` subclass that provides attribute access to its
@@ -246,3 +252,18 @@ Standard names are defined for the following types:
    instead.
 
    .. versionadded:: 3.3
+
+
+.. function:: DynamicClassAttribute(fget=None, fset=None, fdel=None, doc=None)
+
+   Route attribute access on a class to __getattr__.
+
+   This is a descriptor, used to define attributes that act differently when
+   accessed through an instance and through a class.  Instance access remains
+   normal, but access to an attribute through a class will be routed to the
+   class's __getattr__ method; this is done by raising AttributeError.
+
+   This allows one to have properties active on an instance, and have virtual
+   attributes on the class with the same name (see Enum for an example).
+
+   .. versionadded:: 3.4

Doc/whatsnew/3.4.rst

@@ -1270,6 +1270,17 @@ reducing the amount of memory consumed.  (Contributed by Andrew Kuchling in
 :issue:`1565525`).
 
 
+types
+-----
+
+A new :func:`~types.DynamicClassAttribute` descriptor provides a way to define
+an attribute that acts normally when looked up through an instance object, but
+which is routed to the *class* ``__getattr__`` when looked up through the
+class.  This allows one to have properties active on a class, and have virtual
+attributes on the class with the same name (see :mod:`Enum` for an example).
+(Contributed by Ethan Furman in :issue:`19030`.)
+
+
 urllib
 ------
 
@@ -1512,6 +1523,12 @@ Other Build and C API Changes
   object allocator have been silenced.  (Contributed by Dhiru Kholia in
   :issue:`18596`.)
 
+* New function :c:func:`Py_SetStandardStreamEncoding` allows an application
+  that is embedding Python to do the equivalent of setting
+  :envvar:`PYTHONIOENCODING`.  Its arguments override the equivalent
+  values from :envvar:`PYTHONIOENCODING` if it exists.  (Contributed
+  by Bastien Montagne and Nick Coghlan in :issue:`16129`.)
+
 
 .. _other-improvements-3.4: