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Using alternative PyObject* in dynamically created classes

Ronald Oussoren ronaldoussoren at mac.com
Tue Nov 23 16:07:12 EST 2004 
On 23-nov-04, at 14:07, Jacek Generowicz wrote:

> Jacek Generowicz <jacek.generowicz at cern.ch> writes:
>
>> I would like some of my _dynamically_ created new-style classes to
>> have instances which are not represented by the standard PyObject, but
>> one which has an extra void* slot which I want to use for my nefarious
>> purposes, in extension functions. The pointer need not be initialized
>> (for now) I just want it to be there in case I want to stuff something
>> in there later on in the run.
>>
>> What is the laziest way of achieving this?
>>
>> As far as I can tell, PyTypeObject (and its allocators, deallocators,
>> methods in general) only refer to the type of the instance struct via
>> tp_basicsize (where only the struct's size is held).
>>
>> So my first attempt merely resets tp_basicsize to the size of my
>> alternative instance struct, as soon as the class is created. This
>> goes horribly wrong when instances of the class are deallocated, but I
>> can't see why.
>>
>> Where else must I provide information about the instance struct type ?
>>
>>
>> [I will be away for a few days, from a few hours from now; please
>> don't take a long response time as a sign of rudeness.]
>
>
> Hmm ... no takers ?
>
> :-(

Appearently not :-).

Do you want to create those classes in Python, or from your extension 
module? If you create the class in C its easy to add a hidden slot. You 
can even add a field to the type object that contains the location of 
that hidden slot.

Ronald
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