[Python-Dev] Class destructor (original) (raw)

Nick Maclaren nmm1 at cus.cam.ac.uk
Wed Feb 28 18:24:57 CET 2007

"Phillip J. Eby" <pje at telecommunity.com> wrote:

>But I need to clean up workspace when a class (not object) is >deallocated. I can't easily use attributes, as people suggested, >because there is no anonymous storage built-in type. I could subvert >one of the existing storage types (buffer, string etc.), but that is >unclean. And I could write one, but that is excessive. > >So far, I have been unable to track down how to get something called >when a class is destroyed. The obvious attempts all didn't work, in >a variety of ways. Surely there must be a method? This could be in >either Python or C. Have you tried a PyCObject? This is pretty much what they're for:

Oh, yes, I use them in several places, but they don't really help.

Their first problem is that they take a 'void *' and not a request for space, so I have to allocate and deallocate the space manually. Now, I could add a destructor to each of them and do that, but it isn't really much prettier than subverting one of the semi-generic storage types for an improper purpose!

It would be a heck of a lot cleaner to deallocate all of my space in exactly the converse way that I allocate and initialise it. It would also all me to collect and log statistics, should I so choose. This could be VERY useful for tuning! I haven't done that, yet, but might well do so.

All in all, what I need is some way to get a callback when a class object is destroyed. Well, actually, any time from its last use for object work and the time that its space is reclaimed - I don't need any more precise time than that.

I suppose that I could add a C object as an attribute that points to a block of memory that contains copies of all my workspace pointers, and use the object deallocator to clean up. If all else fails, I will try that, but it seems a hell of a long way round for what I would have thought was a basic requirement.

Regards, Nick Maclaren, University of Cambridge Computing Service, New Museums Site, Pembroke Street, Cambridge CB2 3QH, England. Email: nmm1 at cam.ac.uk Tel.: +44 1223 334761 Fax: +44 1223 334679

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