:mod:`Bastion` --- Restricting access to objects
================================================

.. module:: Bastion
   :synopsis: Providing restricted access to objects.
.. moduleauthor:: Barry Warsaw <bwarsaw@python.org>


.. versionchanged:: 2.3
   Disabled module.

.. warning::

   The documentation has been left in place to help in reading old code that uses
   the module.

According to the dictionary, a bastion is "a fortified area or position", or
"something that is considered a stronghold."  It's a suitable name for this
module, which provides a way to forbid access to certain attributes of an
object.  It must always be used with the :mod:`rexec` module, in order to allow
restricted-mode programs access to certain safe attributes of an object, while
denying access to other, unsafe attributes.

.. % I'm concerned that the word 'bastion' won't be understood by people
.. % for whom English is a second language, making the module name
.. % somewhat mysterious.  Thus, the brief definition... --amk

.. % I've punted on the issue of documenting keyword arguments for now.


.. function:: Bastion(object[, filter[, name[, class]]])

   Protect the object *object*, returning a bastion for the object.  Any attempt to
   access one of the object's attributes will have to be approved by the *filter*
   function; if the access is denied an :exc:`AttributeError` exception will be
   raised.

   If present, *filter* must be a function that accepts a string containing an
   attribute name, and returns true if access to that attribute will be permitted;
   if *filter* returns false, the access is denied.  The default filter denies
   access to any function beginning with an underscore (``'_'``).  The bastion's
   string representation will be ``<Bastion for name>`` if a value for *name* is
   provided; otherwise, ``repr(object)`` will be used.

   *class*, if present, should be a subclass of :class:`BastionClass`;  see the
   code in :file:`bastion.py` for the details.  Overriding the default
   :class:`BastionClass` will rarely be required.


.. class:: BastionClass(getfunc, name)

   Class which actually implements bastion objects.  This is the default class used
   by :func:`Bastion`.  The *getfunc* parameter is a function which returns the
   value of an attribute which should be exposed to the restricted execution
   environment when called with the name of the attribute as the only parameter.
   *name* is used to construct the :func:`repr` of the :class:`BastionClass`
   instance.