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<H1><A NAME="SECTION0019200000000000000000">
17.2 <tt class="module">Bastion</tt> --
Restricting access to objects</A>
</H1>
<P>
<A NAME="module-Bastion"></A>
<span class="versionnote">Changed in version 2.3:
Disabled module.</span>
<P>
<div class="warning"><b class="label">Warning:</b>
The documentation has been left in place to help in reading old code
that uses the module.
</div>
<P>
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
<tt class="module"><a href="module-rexec.html">rexec</a></tt> module, in order to allow restricted-mode programs
access to certain safe attributes of an object, while denying access
to other, unsafe attributes.
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4934' xml:id='l2h-4934' class="function">Bastion</tt></b>(</nobr></td>
<td><var>object</var><big>[</big><var>, filter</var><big>[</big><var>,
name</var><big>[</big><var>, class</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Protect the object <var>object</var>, returning a bastion for the
object. Any attempt to access one of the object's attributes will
have to be approved by the <var>filter</var> function; if the access is
denied an <tt class="exception">AttributeError</tt> exception will be raised.
<P>
If present, <var>filter</var> must be a function that accepts a string
containing an attribute name, and returns true if access to that
attribute will be permitted; if <var>filter</var> returns false, the access
is denied. The default filter denies access to any function beginning
with an underscore ("<tt class="character">_</tt>"). The bastion's string representation
will be "<tt class="samp"><Bastion for <var>name</var>></tt>" if a value for
<var>name</var> is provided; otherwise, "<tt class="samp">repr(<var>object</var>)</tt>" will be
used.
<P>
<var>class</var>, if present, should be a subclass of <tt class="class">BastionClass</tt>;
see the code in <span class="file">bastion.py</span> for the details. Overriding the
default <tt class="class">BastionClass</tt> will rarely be required.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><span class="typelabel">class</span> <tt id='l2h-4935' xml:id='l2h-4935' class="class">BastionClass</tt></b>(</nobr></td>
<td><var>getfunc, name</var>)</td></tr></table></dt>
<dd>
Class which actually implements bastion objects. This is the default
class used by <tt class="function">Bastion()</tt>. The <var>getfunc</var> 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. <var>name</var> is used to
construct the <tt class="function">repr()</tt> of the <tt class="class">BastionClass</tt> instance.
</dl>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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