Doc/lib/libbastion.tex

   1 \section{\module{Bastion} ---
   2          Restricting access to objects}
   3
   4 \declaremodule{standard}{Bastion}
   5 \modulesynopsis{Providing restricted access to objects.}
   6 \moduleauthor{Barry Warsaw}{bwarsaw@python.org}
   7 \versionchanged[Disabled module]{2.3}
   8
   9 \begin{notice}[warning]
  10   The documentation has been left in place to help in reading old code
  11   that uses the module.
  12 \end{notice}
  13
  14 % I'm concerned that the word 'bastion' won't be understood by people
  15 % for whom English is a second language, making the module name
  16 % somewhat mysterious.  Thus, the brief definition... --amk
  17
  18 According to the dictionary, a bastion is ``a fortified area or
  19 position'', or ``something that is considered a stronghold.''  It's a
  20 suitable name for this module, which provides a way to forbid access
  21 to certain attributes of an object.  It must always be used with the
  22 \refmodule{rexec} module, in order to allow restricted-mode programs
  23 access to certain safe attributes of an object, while denying access
  24 to other, unsafe attributes.
  25
  26 % I've punted on the issue of documenting keyword arguments for now.
  27
  28 \begin{funcdesc}{Bastion}{object\optional{, filter\optional{,
  29                           name\optional{, class}}}}
  30 Protect the object \var{object}, returning a bastion for the
  31 object.  Any attempt to access one of the object's attributes will
  32 have to be approved by the \var{filter} function; if the access is
  33 denied an \exception{AttributeError} exception will be raised.
  34
  35 If present, \var{filter} must be a function that accepts a string
  36 containing an attribute name, and returns true if access to that
  37 attribute will be permitted; if \var{filter} returns false, the access
  38 is denied.  The default filter denies access to any function beginning
  39 with an underscore (\character{_}).  The bastion's string representation
  40 will be \samp{<Bastion for \var{name}>} if a value for
  41 \var{name} is provided; otherwise, \samp{repr(\var{object})} will be
  42 used.
  43
  44 \var{class}, if present, should be a subclass of \class{BastionClass};
  45 see the code in \file{bastion.py} for the details.  Overriding the
  46 default \class{BastionClass} will rarely be required.
  47 \end{funcdesc}
  48
  49
  50 \begin{classdesc}{BastionClass}{getfunc, name}
  51 Class which actually implements bastion objects.  This is the default
  52 class used by \function{Bastion()}.  The \var{getfunc} parameter is a
  53 function which returns the value of an attribute which should be
  54 exposed to the restricted execution environment when called with the
  55 name of the attribute as the only parameter.  \var{name} is used to
  56 construct the \function{repr()} of the \class{BastionClass} instance.
  57 \end{classdesc}