Python's interactive mode is one of the implementation's great
strengths -- being able to write expressions on the command line
and get back a meaningful output. However, the output function
cannot be all things to all people, and the current output
function too often falls short of this goal. This PEP describes a
way to provides alternatives to the built-in display function in
Python, so users will have control over the output from the
The current Python solution has worked for many users, and this
should not break it. Therefore, in the default configuration,
nothing will change in the REPL loop. To change the way the
interpreter prints interactively entered expressions, users
will have to rebind sys.displayhook to a callable object.
The result of calling this object with the result of the
interactively entered expression should be print-able,
and this is what will be printed on sys.stdout.
The bytecode PRINT_EXPR will call sys.displayhook(POP())
A displayhook() will be added to the sys builtin module, which is
if o is None:
__builtin__._ = None
__builtin__._ = o
The method Py.printResult will be similarily changed.