Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Terry Reedy <tjreedy@udel.edu>
Newsgroups: comp.lang.python
Subject: Re: Accessing container's methods
Date: Mon, 7 Dec 2015 16:38:33 -0500
Lines: 56
Message-ID: <mailman.31.1449524372.12405.python-list@python.org>
References: <dcm0c2Fi2ktU1@mid.individual.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0
In-Reply-To: <dcm0c2Fi2ktU1@mid.individual.net>
Precedence: list
Xref: csiph.com comp.lang.python:100109

On 12/7/2015 1:10 PM, Tony van der Hoff wrote:
> Hi,
>
> I have a class A, containing embedded embedded classes, which need to
> access methods from A.
> .
> 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.
>
> I don't really want to make Actor a sub-class (is-a; it isn't) of Monty;
> that would raise all sorts of other problems.
>
> Can anyone please advise me on how to achieve this magic?
>
> # define the outer class
> class Monty:
>    def __init__( self, names ):
>      self.actors = []
>
>      i = 0
>      for n in names:
>        self.actors.append( Actor( n, i ) )
>        i += 1    # here is a case for python supporting post-increment!

This is actually a case for using enumerate:
   for i, name in enumerate(names):

>
>    def count_actors( self ):
>      return len( self.actors )
>
>    def list_actors( self ):
>      h=[]
>      for n in self.actors:
>        h.append( n.get_name() )
>      return h

return list(self.actors)  # or perhaps even faster
return self.actors[:]

> # define the inner class
> class Actor:
>    def __init__ ( self, name, id ):
>      self.name = name
>      self.id = id

Tkinter, and I presume tk, works by creating circular references.
widgets get a reference to a master widget, and container get a 
reference to widgets that are placed (or packed or gridded) therein. 
Widgets have an explicit .destroy method (inherited from tcl/tk) to undo 
the circularity.  It works, but it is not completely without problems.

-- 
Terry Jan Reedy