Path: csiph.com!usenet.pasdenom.info!gegeweb.org!de-l.enfer-du-nord.net!feeder1.enfer-du-nord.net!rt.uk.eu.org!feed.xsnews.nl!border-1.ams.xsnews.nl!xlned.com!feeder7.xlned.com!news2.euro.net!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
To: python-list@python.org
From: Peter Otten <__peter__@web.de>
Subject: Re: Nice solution wanted: Hide internal interfaces
Date: Mon, 29 Oct 2012 18:06:30 +0100
Organization: None
References: <k6mb4k$5v3$1@news.albasani.net>
Mime-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7Bit
User-Agent: KNode/4.7.3
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.3032.1351530395.27098.python-list@python.org>
Lines: 35
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:32404

Johannes Bauer wrote:

> Now I want A to call some private methods of B and vice versa (i.e. what
> C++ "friends" are), but I want to make it hard for the user to call
> these private methods.
> 
> Currently my ugly approach is this: I delare the internal methods
> private (hide from user). Then I have a function which gives me a
> dictionary of callbacks to the private functions of the other objects.
> This is in my opinion pretty ugly (but it works and does what I want).
> 
> I'm pretty damn sure there's a nicer (prettier) solution out there, but
> I can't currently think of it. Do you have any hints?

Maybe you  can wrap A into a class that delegates to A:

>>> class A(object):
...     def __private(self): print "private A"
... 
>>> class Friend(object):
...     def __init__(self, obj):
...             self.__obj = obj
...             self.__prefix = "_%s_" % obj.__class__.__name__
...     def __getattr__(self, name):
...             return getattr(self.__obj, self.__prefix + name)
... 
>>> a = A()
>>> a._A__private() # hard
private A
>>> f = Friend(a)
>>> f._private() # easy
private A

The B instance would refer to A via the Friend instance.