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.
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.
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