[Python-Dev] Need advice, maybe support (original) (raw)

Christian Tismer tismer@tismer.com
Tue, 20 May 2003 00:09:14 +0200

Lieber Martin,

Christian Tismer <tismer@tismer.com> writes:

The problem is that I need to give extra semantics to existing objects, which are PyCFunction objects. I think putting an extra bit into the type object doesn't help, unless I use a new type. But then I don't need the flag. An old extension module which is loaded into my Python will always use my PyCFunction, since this is always borrowed. I understand the concern is not about changing PyCFunction, but about changing PyMethodDef, which would get another field.

Exactly. This is the static structure which is lingering around in many old extension modules, and to change it would require massive recompilation.

I think you can avoid adding a field to PyMethodDef, by providing a PyMethodDefEx structure, which has the extra field, and is referred-to from (a new slot in) the type object. The slots in the type object that refer to PyMethodDefs would either get set to NULL, or initialized with a copy of the PyMethodDefEx with the extra field removed.

Hey, that's really not bad!

Today, I've banged my head on my desk many times, trying to find out how to turn a clean, new approach into the least hackish surrogate, which is binary compatible. Well, I found some, not really pretty but working. It uses not an extra field, but extra records, which are used as sibling fields, past the end of the method table.

I have to think about what implementation is more efficient, and uses less of my resources. Since Guido donated 8+1 bits to me, I have a big degree of freedom about how I will implement things in the future.

Maybe I'd go ahead and see these bits checked in ASAP, and then re-think the design. Perhaps I will give back 8 bits, when I really don't need them, but I really don't know, yet.

thanks anyway -- good idea - chris

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