In preparation for a ``restricted execution mode'' which will be
usable to run code received from an untrusted source (such as a WWW
server or client), the mechanism by which modules are imported has
been redesigned. It is now possible to provide your own function
__import__ which is called whenever an import statement
is executed. There's a built-in function __import__ which
provides the default implementation, but more interesting, the various
steps it takes are available separately from the new built-in module
imp. (See the section on imp in the Library Reference
Manual for more information on this module -- it also contains a
complete example of how to write your own __import__ function.)
When you do dir() in a fresh interactive interpreter you will
see another ``secret'' object that's present in every module:
__builtins__. This is either a dictionary or a module
containing the set of built-in objects used by functions defined in
current module. Although normally all modules are initialized with a
reference to the same dictionary, it is now possible to use a
different set of built-ins on a per-module basis. Together with the
fact that the import statement uses the __import__
function it finds in the importing modules' dictionary of built-ins,
this forms the basis for a future restricted execution mode.