Python Cookbook

Delegating Messages to Multiple Objects

Credit: Eduard Hiti

Problem

You need to multiplex messages (attribute requests) to several objects that share the same interface.

Solution

As usual, this task is best wrapped in a class:

import operator

# faster in Python 2.2, but we also handle any release from 2.0 and later
try: dict
except: from UserDict import UserDict as dict

class Multiplex(dict):
    """ Multiplex messages to registered objects """
    def _ _init_ _(self, objs=[]):
        dict._ _init_ _(self)
        for alias, obj in objs: self[alias] = obj

    def _ _call_ _(self, *args, **kwargs):
        """ Call registered objects and return results through another
        Multiplex. """
        return self._ _class_ _( [ (alias, obj(*args, **kwargs))
            for alias, obj in self.items(  ) ] )

    def _ _nonzero_ _(self):
        """ A Multiplex is true if all registered objects are true. """
        return reduce(operator.and_, self.values(  ), 1)

    def _ _getattr_ _(self, name):
        """ Wrap requested attributes for further processing. """
        try: return dict._ _getattr_ _(self, name)
        except:
            # Return another Multiplex of the requested attributes
            return self._ _class_ _( [ (alias, getattr(obj, name) )
                for alias, obj in self.items(  ) ] )

As usual, this module is also invokable as a script, and, when run that way, supplies a self-test (or, here, a demo/example):

if _ _name_ _ == "_ _main_ _": import StringIO file1 = StringIO.StringIO( ) file2 = StringIO.StringIO( ) delegate = Multiplex( ) delegate[id(file1)] = file1 delegate[id(file2)] = file2 assert not delegate.closed ...