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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.python
Subject: Re: Accessing container's methods
Date: Tue, 08 Dec 2015 20:02:10 +0100
Organization: PointedEars Software (PES)
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Erik wrote:
^^^^
Please fix, Erik #75656.

> On 07/12/15 18:10, Tony van der Hoff wrote:
>> A highly contrived example, where I'm setting up an outer class in a
>> Has-a relationship, containing a number of Actors. The inner class needs
>> to access a method of the outer class; here the method get_name.
> 
> Generally, an object should not need to know which container it's in

NAK.  All kinds of objects already "know" which container they are in.

> (let alone its "index" or "key" in that container).

That is a different issue.

> Amongst other things, you can't put the object into multiple containers

You could if you made it a list of container references.

> which might be organised differently and you are asking for bugs where the
> container and the object get out of sync WRT just where the object is in 
> the container

It is the container’s job to make sure that this does not happen.

>> Can anyone please advise me on how to achieve this magic?
> 
> As you can't sensibly put the object into more than one container at a
> time anyway,

You can.  Quickhack:

class Child:
    self._parents = []

    def add_to_parent (self, parent):
        self._parents.append(parent)
        self._parents = list(set(self._parents))

    def get_parents (self)
        return self._parents

class Parent:
    self._children = []

    def add_child (self, child):
        self._children.append(child)
        child.add_to_parent(self)

| >>> p = Parent()
| >>> c = Child()
| >>> p.add_child(c)
| >>> p2 = Parent()
| >>> p2.add_child(c)
| >>> c.get_parents()
| [p, p2]

“As a child, I want to know who my parents are.”

Certainly you will not deny the validity of that user story ;-)

-- 
PointedEars

Twitter: @PointedEars2
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