It also directly addresses the question of aliasing. Think about how Steven's modified dictionary would react to this code:
pete = CreateRobot(2, 3) dad = pete dad.move() pete.move()
If you'd like to handle these cases, but you don't want to have to explain aliasing right off the bat, you could try something like:
py> class Robot(object): ... def __init__(self): ... self.names = set() ... def move(self): ... if len(self.names) == 1: ... name, = self.names ... print "robot with name %r moved" % name ... else: ... print "robot with names %r moved" % sorted(self.names) ... py> class RobotDict(dict): ... def __setitem__(self, name, value): ... if isinstance(value, Robot): ... value.names.add(name) ... super(RobotDict, self).__setitem__(name, value) ... py> user_code = """\ ... nick = Robot() ... pete = Robot() ... dad = pete ... nick.move() ... dad.move() ... pete.move()""" py> exec user_code in RobotDict(Robot=Robot) robot with name 'nick' moved robot with names ['dad', 'pete'] moved robot with names ['dad', 'pete'] moved
That is, you can just keep track of all the names of a Robot in the Robot object. In the simple case, where there's only one name, you can display it as such. In the more complicated case, where there's some aliasing, you can display the multiple aliases. This means you don't have to teach about aliasing right off the bat, but if a student accidentally discovers it on their own, the machinery's there to explain it...
Steve -- http://mail.python.org/mailman/listinfo/python-list
