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From: "Frank Millman" <frank@chagford.com>
Subject: Re: Self healthcheck
Date: Thu, 23 Jan 2014 07:36:53 +0200
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"Asaf Las" <roegltd@gmail.com> wrote in message 
news:9729ddaa-5976-4e53-8584-6198b47b6789@googlegroups.com...
> On Wednesday, January 22, 2014 10:56:30 AM UTC+2, Frank Millman wrote:
>>
>> class MainObject:
>>     def __init__(self, identifier):
>>          self._del = delwatcher('MainObject', identifier)
>> class delwatcher:
>>     def __init__(self, obj_type, identifier):
>>         self.obj_type = obj_type
>>         self.identifier = identifier
>>         log('{}: id={} created'.format(self.obj_type, self.identifier))
>>     def __del__(self):
>>         log('{}: id={} deleted'.format(self.obj_type, self.identifier))
>> If you do find that an object is not being deleted, it is then
>> trial-and-error to find the problem and fix it. It is probably a circular
>> reference
>>
>> Frank Millman
>
> Thanks Frank. Good approach!
>
> One question - You could do:
> class MainObject:
>    def __init__(self, identifier):
>         self._del = delwatcher(self)
> then later
>
> class delwatcher:
>    def __init__(self, tobject):
>        self.obj_type = type(tobject)
>        self.identifier = id(tobject)
>        ...
>
> when creating delwatcher. Was there special reason to not to use them?
> is this because of memory is reused when objects are deleted
> and created again so same reference could be for objects created
> in different time slots?
>

I read Dave's reply, and he is correct in saying that id's are frequently 
re-used in python.

However, in this particular case, I think you are right, it is safe to use 
the id to identify the object. An id can only be re-used if the original 
object is deleted, and that is the whole point of this exercise. We expect 
to see the id come up in a 'created' message, and then the same id appear in 
a 'deleted' message. If this happens, we are not concerned if the same id 
reappears in a subsequent 'created' message.

Frank