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<title>17.2 Bastion -- Restricting access to objects
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<H1><A NAME=
"SECTION0019200000000000000000">
17.2 <tt class=
"module">Bastion
</tt> --
Restricting access to objects
</A>
<A NAME=
"module-Bastion"></A>
<span class=
"versionnote">Changed in version
2.3:
<div class=
"warning"><b class=
"label">Warning:
</b>
The documentation has been left in place to help in reading old code
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.
<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>
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.
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
<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><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>
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.
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<span class=
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2.4.2, documentation updated on
28 September
2005.
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