30.2. "Bastion" — Restricting access to objects
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2.6 版後已棄用: The "Bastion" module has been removed in Python 3.

2.3 版更變: Disabled module.

備註: 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
"rexec" module, in order to allow restricted-mode programs access to
certain safe attributes of an object, while denying access to other,
unsafe attributes.

Bastion.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
   "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 "BastionClass";  see
   the code in "bastion.py" for the details.  Overriding the default
   "BastionClass" will rarely be required.

class Bastion.BastionClass(getfunc, name)

   Class which actually implements bastion objects.  This is the
   default class used by "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 "repr()" of the "BastionClass" instance.
