A question about fill_free_list(void) function

Christian Heimes lists at cheimes.de
Wed Jul 1 14:01:55 EDT 2009

Pedram schrieb:
> Hello community,
> I'm reading the CPython interpreter source code,
> first, if you have something that I should know for better reading
> this source code, I would much appreciate that :)
> second, in intobject.c file, I read the following code in
> fill_free_list function that I couldn't understand:
> <code>while (--q > p)
>     Py_TYPE(q) = (struct _typeobject *)(q-1);
> Py_TYPE(q) = NULL;
> </code>
> What does it mean?

The code is abusing the ob_type member to store a single linked, NULL
terminated list of free integer objects. It's a tricky optimization you
don't have to understand in order to understand the rest of the code.

And no, the code in ctypes.h is totally unrelated to the free list in


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