insanity.py

from django.db import models

class DeviceA(object):
    def do_something(self, string='Hello'):
        print "Device A something '%s'" % string

    def do_something_else(self):
        print "Device A something else"


class DeviceB(object):
    def do_something(self, string='Hello'):
        print "Device B something '%s'" % string

    def do_something_else(self):
        print "Device B something else"


class DeviceC(object):
    def do_something(self, string='Hello'):
        print "Device C something '%s'" % string

    def do_something_else(self):
        print "Device C something else"


class Device(models.Model):
    _device_class = None
    DEVICE_TYPES = (
        ('A', 'Device A'),
        ('B', 'Device B'),
        ('C', 'Device C'),
    )
    type = models.CharField(max_length=1, choices=DEVICE_TYPES)

    def __init__(self, *args, **kwargs):
        super(Device, self).__init__(*args, **kwargs)
        if self.type == 'A':
            self._device_class = DeviceA

        elif self.type == 'B':
            self._device_class = DeviceB

        elif self.type == 'C':
            self._device_class = DeviceC

    def __getattr__(self, name):
        if hasattr(self._device_class, name):
            return self._device_class.__getattribute__(name)

    def __setattr__(self, *args, **kwargs):
        return self._device_class.__setattr__(*args, **kwargs)