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.
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
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 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.