[Python-Dev] PyInstance_Check() and new-style classes

Eric Wilhelm ewilhelm at sbcglobal.net
Mon Jul 12 18:48:25 CEST 2004

# The following was supposedly scribed by
# Michael Hudson
# on Monday 12 July 2004 09:14 am:

>Eric Wilhelm <ewilhelm at sbcglobal.net> writes:
>> For starters, the process-of-elimination way of determining the type is
>> pretty clunky, and only works on classes which have subclassed the
>> 'object' type (not lists, tuples, strings, etc.)
>That just restates the problem :-) *Why* do you care if a given object
>is an instance of a builtin type or not?

I only care that it is an instance of a user-defined class, so that the 
Inline::Python module can bless a reference to its memory address, which then 
allows Perl to locate the bound methods in the symbol table.

>>>but checking the TP_HEAPTYPE flag in tp_flags may go
>>>some way towards one.
>> I'll have to look into this.  I'm not sure what that would tell me.
>Well, it tells you whether the type objects memory lives on the heap
>or is a static object from the C point of view.  This is potentially
>interesting because it being true is /almost/ synonmous with
>'user-defined type'.

Are there some other serpents lurking in that /almost/ besides the 
"C-extensions" one?   If not, I think we can accept the simple work-around of 
defining an empty python subclass (e.g. 'pass') (see my reply to Phillip's 

>What you do with subclasses of builtin types like strings is a
>difficult question.  I wouldn't presume to know the best thing to do

Ideally, I'd like them to be a proper Perl reference to a Perl scalar 
containing the string.  Though this is really more important for tuples and 
lists than it is for strings.  As it is, my new code will identify anything 
which comes from a classic or new-style class (with the caveat (supposedly) 
that the new-style class was not created as a C extension) and return a 
reference to a scalar which contains the memory address of the object (be it 
an instance or a type.)

Yes, this means that classes which subclass tuples or lists will appear as 
opaque objects in Perl (accessible only via their methods), but I think 
that's acceptable.

"It ain't those parts of the Bible that I can't understand that 
bother me, it's the parts that I do understand."
                                        --Mark Twain

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