python destructor

Ferencik Ioan ferencikioan at gmail.com
Mon Nov 5 07:51:00 CET 2012


Hello there folks,

I have a bit of a special issue.
I'll start by disclosing myself for what i am doing. I am a postgraduate student and I really have good reasons to do what I am doing. At least i think so.

And not the issue.
I am building a python web service. This web service has some generic objects and I use a metaclass to customize the classes. 
Second I use a non-conventional object oriented database, dybase 

(http://www.garret.ru/dybase/doc/dybase.html#introduction)

Now these is a OODBMS claiming to support ACID transactions.


The instances of my objects are recursively organizing themselves into a hierarchical tree-like structure. When I make an instance of this object persistent dybase actually can recursively save all tree structure.
Everything works well here. 

I altered the main class situated at the root of my class hierarchy to actually store inside the__dict__ not the instances of its children but their unique ID's. Then when I set a child attribute I create it and instead of being stored in the instance the child goes to a database index object. Thus it becomes Universally addressable. The a parent retrieves the child it actually fetches it from the database. 
In this way I ended up with very small objects.However these objects can regenerate the treelike structure as if they were storing there children in the __dict__.

The issue is how to give the instances access to the database and properly handle the opening and closing of the database.
It seems futile to me to actually open/close the connection through a context. Because the database is a file it will issue an IO operation on every attribute access and we all know __getattribute__ is used extremely often.
For this reason I thought the best way would be to wrap the dybase Storage (main class) into a local storage version which would have __del__ method.
The local Storage is a new style class..it opens the DB file but the __del__ is never called.
This is because the Storage class has at least 2 cyclic references. 
So my Storage class never closes the database. I would like this class to close the database when it is garbage collected.
The class is a Singleton FYI as well but this might not be relevant or even necessary.
So my question is:
what s the best way to force __del__ on a singleton that has cyclic references. Should i use weakref and alter the original source? Is there a way i can force a singleton to garbage collect itself?.

I am by no means a software engineer so i would appreciate any advice from some experts on the matter.
Thank you in advance.








More information about the Python-list mailing list