Is it possible to refer to the owner class that an object belongs to as an attribute?

I am not quite sure this is possible (or something similar) in python. I want to access a method (or another object) of a class from an object that is an attribute of such class.

Consider the following code:

class A():
def __init__(self):
self.b = B()
self.c = C()
def print_owner(self):
print('owner')

class B():
def __init__(self):
pass
def call_owner(self):
self.owner().print_owner()


so that b as an object attribute of class A, can refer to a method or attribute of A?

b

A

A

Or similarly, is it possible that b can access c?

b

c

self.owner

self.owner()

WeakAttribute

3 Answers
3

It's possible. You can pass a reference to A to B constructor:

...
self.b = B(self)
...

class B:
def __init__(self, a):
self.a = a


So, B.a stores the reference to its owner A.

self.owner

self.a

There can be many references to object B(), not only the one in instance of class A. So it's not possible as it is in your code. (Well you could try a hack, like finding all instances of class A in memory and find the one whose attribute b points to your B instance, but that's a really bad idea).

B()

A

A

b

You should explicitly store in instance of B a reference to the owner.

B

You have a couple of options here. The better one is probably @Sianur suggests. It's simple, effective, and explicit. Give that answer an upvote.

Another option is to have the owner force itself on its minions. B can do something like

B

def call_owner(self):
if hasattr(self, 'owner'):
self.owner().print_owner()
else:
print('I am free!')


Meanwhile, A would set the owner attribute to itself:

A

def __init__(self):
self.b = B()
self.c = C()
self.b.owner = self.c.owner = self


In any case, if you want an object to have access to another object, store the reference into an accessible place. There's no magic here.

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