Question

I’m having some problems with the super function in Python. Suppose I have these two classes:

class A(object):
     x=5
     def p(self):
             print 'A'
     def f(self):
             self.p()
             self.x+=1

class B(A):
    def p(self):
             print 'B'
    def f(self):
             super(B, self).f()
             self.x*=2

b = B()
b.f()

Then b.x will equal 12, but the function will output ‘B’, not ‘A’. What I need is to execute A.p instead of B.p, how can I achieve that?

Thanks for your time 🙂

---

EDIT: Ok, I think you missed some details about my actual situation because of my poor example. Let’s get to real code. I have these two classes (Django models):

class Comment(Insert, models.Model):

    content = models.TextField()
    sender = models.ForeignKey('logic.User')
    sent_on = models.DateTimeField(auto_now_add=True)

    def __insert__(self):
        self.__notify__()

    def __notify__(self):
        receivers = self.retrieve_users()
        notif_type = self.__notificationtype__()
        for user in receivers:
            Notification.objects.create(
                object_id=self.id,
                receiver=user,
                sender_id=self.sender_id,
                type=notif_type
            )

    def __unicode__(self):
        return self.content

    class Meta:
        abstract = True


class UserComment(Comment):

    is_reply = models.BooleanField()
    reply_to = models.ForeignKey('self', blank=True,
                                null=True, related_name='replies')
    receiver = models.ForeignKey('User', related_name='comments')

    def __insert__(self):
        super(UserComment, self).__insert__()
        self.__notify__()

    def __notification__(self, notification):
        if self.is_reply:
            return '%s has replied your comment' % self.sender
        return super(UserComment, self).__notification__(notification)

    def __notify__(self):
        # Notification objects "should" be created by Comment's __notify__
        Update.objects.create(
            object_id=self.id,
            target=self.receiver,
            type=self.__updatetype__(),
        )

    @classmethod
    @cache(prop_name='_notificationtype')
    def __notificationtype__(cls):
        return NotificationType.objects.get(name='USER_COMMENT')

    @classmethod
    @cache(prop_name='_updatetype')
    def __updatetype__(cls):
        return UpdateType.objects.get(name='USER_COMMENT')

    def retrieve_users(self):
        return [self.receiver]  # retrieve_users MUST return an iterable

The problem is with __insert__ and __notify__ methods on both models. __insert__ is a method that gets called the first time an object is recorded to the DB, and I use it for notification purposes mainly. Then, this is what I want to do:

1. Create a UserComment object and save it
2. Call UserComment instance’s __insert__
3. Call Comment’s __insert__, which should call Comment’s __notify__
4. Call UserComment instance’s __notify__ from __insert__

Is this possible in a more or less easy way or do I have to refactor my code?
Thanks again for all your answers.

Answer 1

Remember that self refers to an instance and since b is an instance of B, self.p() refers to method p() in class B, not A. So either remove method p() from class B or explicitly call A's p() from B as:

class B(A):
    def p(self):
             super(B, self).p()
             print 'B'
    def f(self):
             super(B, self).f()
             self.x*=2

Or make p a staticmethod of A and call it from f() in class A with A.p(), especially if you don’t need access to the class from that method making p a ‘function’ rather than a ‘method’:

class A(object):
    x=5
    @staticmethod
    def p():
        print 'A'
    def f(self):
        A.p()
        self.x+=1

With this B, the output is:

>>> b = B()
>>> b.f()
A
>>> b.x
12
>>> b.p()
A
B

Note how B got printed only in the b.p() call but not when it was b.f().