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