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

Eric Wilhelm ewilhelm at sbcglobal.net
Mon Jul 12 18:37:40 CEST 2004

The following was supposedly scribed by

Phillip J. Eby

on Monday 12 July 2004 11:12 am:

I'm not sure if I understand what this flag is telling me.  According to the api/type-structs.html, PyTPFLAGSHEAPTYPE is set when the object is allocated.  To me, that reads that it would be set for builtin tuples, etc even if they were not subclassed. A "heap type" is a type whose type struct is in heap memory.  A "non-heap" type is one whose type struct is declared statically, i.e. in C code. So, a non-heap type is either a built-in type, or an extension type provided by a C extension module.  A heap type is either one coded in pure Python, or potentially a C extension coded in an unusual fashion (e.g. via Pyrex).

Okay, looks like this will work just beautifully. Heaptype is true for an instance of a class which inherits from a builtin type, but not for a simple instance of a builtin type.

True, if I were trying to wrap a C extension module via Inline::Python, heaptype would not be true, but a really easy work-around should exist by simply defining a python class which does nothing but inherit the C extension. That would give the Inline::Python code something to grab onto.

Anyway, this is much cleaner:

http://ericwilhelm.homeip.net/svn/Inline-Python/trunk/xs-based/py2pl.c

<snip lots of PyFoo_Check(obj) + lines>

    /* wrap an instance of a Python class */
    /* elw: here we need to make these look like instances: */

PyInstance_Check(obj)) {

PyInstance_Check(obj)) {

So, I think, with everybody's help, I may have found "the right way" (TM.)

Should this be better documented, or is this an obscure usage? Will it break in future versions of Python?

Thanks, Eric

I arise in the morning torn between a desire to improve the world and a desire to enjoy the world. This makes it hard to plan the day. --E.B. White

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