[Python-Dev] another Py_TPFLAGS_HEAPTYPE question

"Martin v. Löwis" martin at v.loewis.de
Mon Aug 17 08:53:56 CEST 2009

> Thanks for the pointer.  I noticed that subtype_dealloc is only called for types
> that are allocated using type_new().  Does this mean that it is not
> safe to create
> types in C using just PyType_Ready() and set Py_TPFLAGS_HEAPTYPE on
> them?  The documentation is not clear on this point.

As Benjamin says, this is getting off-topic - python-dev is not a place
to ask for help in your project.

I believe setting flags on a type is inherently unsafe.

> Here is what I would like to do when I create my types dynamically:
> - implement tp_alloc and tp_dealloc() to INCREF and DECREF the type.
> - not set Py_TPFLAGS_HEAPTYPE.
> - set Py_TPFLAGS_HAVE_GC (because instances of my obj can create cycles)
> Does this seem safe?  I notice that subtype_dealloc() does some funky
> GC/trashcan stuff.  Is it safe for me not to call subtype_dealloc?  Can I
> safely implement my tp_dealloc function like this?

If you bypass documented API, you really need to study the code,
understand its motivation, judge whether certain usage is "safe" wrt.
to the current implementation, and judge the likelihood of this code
not getting changed in future versions.


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