[Python-checkins] r66512 - python/trunk/Doc/library/functions.rst

[raymond.hettinger]

Author: raymond.hettinger
Date: Fri Sep 19 10:07:48 2008
New Revision: 66512

Log:
Improve docs for super().

Modified:
   python/trunk/Doc/library/functions.rst

Modified: python/trunk/Doc/library/functions.rst
==============================================================================
--- python/trunk/Doc/library/functions.rst	(original)
+++ python/trunk/Doc/library/functions.rst	Fri Sep 19 10:07:48 2008
@@ -1216,13 +1216,28 @@
 .. function:: super(type[, object-or-type])
 
    Return a "super" object that acts like the superclass of *type*.
+
    If the second argument is omitted the super
    object returned is unbound.  If the second argument is an object,
    ``isinstance(obj, type)`` must be true.  If the second argument is a type,
    ``issubclass(type2, type)`` must be true. :func:`super` only works for
    :term:`new-style class`\es.
 
-   A typical use for calling a cooperative superclass method is::
+   There are two typical use cases for "super".  In a class hierarchy with
+   single inheritance, "super" can be used to refer to parent classes without
+   naming them explicitly, thus making the code more maintainable.  This use
+   closely parallels the use of "super" in other programming languages.
+   
+   The second use case is to support cooperative multiple inheritence in a
+   dynamic execution environment.  This use case is unique to Python and is 
+   not found in statically compiled languages or languages that only support 
+   single inheritance.  This makes in possible to implement "diamond diagrams"
+   where multiple base classes implement the same method.  Good design dictates
+   that this method have the same calling signature in every case (because the
+   order of parent calls is determined at runtime and because that order adapts
+   to changes in the class hierarchy).
+
+   For both use cases, a typical superclass call looks like this::
 
       class C(B):
           def meth(self, arg):
@@ -1230,6 +1245,8 @@
 
    Note that :func:`super` is implemented as part of the binding process for
    explicit dotted attribute lookups such as ``super(C, self).__getitem__(name)``.
+   It does so by implementing its own :meth:`__getattribute__` method for searching
+   parent classes in a predictable order that supports cooperative multiple inheritance.
    Accordingly, :func:`super` is undefined for implicit lookups using statements or
    operators such as ``super(C, self)[name]``.