Determine the container class of an object in Python 3

[Steve D'Aprano]

On Thu, 26 Oct 2017 12:25 pm, qrious wrote:

> Class1 is instantiated in Class2 as follows. Class2 also contains another
> variable, say:
> 
> class Class2:
>     class1 = Class1()
>     a = 0
> 
> I want to create a method myDef() in Class1 that can read or write to a. How
> do I access a from within myDef() to access a?

The only way is to hard-code the name "Class2" in myDef.

But the usual way to fix this problem is:


class Class1:
    def __init__(self, owner):
        self.owner = owner
    def myDef(self):
        return self.owner.a


def Class2:
    def __init__(self):
        self.class1 = Class1(self)
        self.a = 0

Technically, it is a circular reference, but don't worry about it, Python's
garbage collector can resolve such circular references. If it becomes a
problem -- and it shouldn't, but if it does -- you can use a weakref. But
seriously, don't worry about it unless you need to.

Another solution is to make Class1 a mixin, and then rely on inheritence:

class MyMixin:
    def myDef(self):
        return self.a

class Class2(MyMixin):
    def __init__(self):
        self.a = 0



-- 
Steve
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.