Django - Custom virtual model field with companion stored field [closed]

class MyModel(models.Model):
    confirmation = ConfirmationField()


m = MyModel()
m.confirmation # False
m.confirmation_timestamp # None

m.confirmation = True
m.save()

m.confirmation_timestamp # datetime object


m.confirmation = False
m.save()

m.confirmation_timestamp # None again

def get_attname(self):
    return '%s_id' % self.name

if self.field.width_field:
        setattr(self.instance, self.field.width_field, self.width)
    if self.field.height_field:
        setattr(self.instance, self.field.height_field, self.height)

value = {'BooleanField': True,
             'DateTimeField': datetime.datetime.now(),
             'DateField': datetime.date.today(),
             'IntegerField': 1,
            }[instance._meta.get_field(field_name).get_internal_type()]
    setattr(instance, field_name, value)

class Modelname(models.Model):
    """(Modelname description)"""

    confirmation_timestamp = models.DateTimeField(blank=True)

    def _set_confirmation(self, value):
        if not value:
            self.confirmation_timestamp = None
        else:
            self.confirmation_timestamp = datetime.datetime.now()

    def _get_confirmation(self):
        return bool(self.confirmation_timestamp)

    confirmation = property(_get_confirmation, _set_confirmation)
    confirmation.short_description = "Confirmation"
    confirmation.boolean = True # have it nicely displayed in admin