[Python-3000] PyObject_HEAD_INIT

[M.-A. Lemburg]

On 2008-11-14 22:15, Roger Binns wrote:
> My confusion was because I though that the HEAD for the data structure
> had to use the same corresponding HEAD_INIT in the type.  So for
> whatever reason the PyTypeObject is declared as a var object which is
> why the var HEAD_INIT is needed.
> 
> It still looks like PyObject_HEAD_INIT should be removed so that people
> using earlier versions of Python, following the Py3 docs (before they
> are fixed), using older tutorials etc don't get burnt.
> 
> Grepping through the py3 source shows only PyModuleDef_HEAD_INIT using
> PyObject_HEAD_INIT.  There are no other legitimate uses!

Except maybe a few thousand extensions already using it which are
waiting to be ported to Python 3.

Whether you write:

{PyObject_HEAD_INIT(0), 0, ...

or

{PyVarObject_HEAD_INIT(0, 0), ...

for your type definition doesn't really make much difference. They
both unwrap to the same code. Since PyTypeObjects are variable length
objects, you always need the ob_size entry.

However, the macros exist to be used for both variable size
and fixed size objects, so having both available is useful and
legitimate.

-- 
Marc-Andre Lemburg
eGenix.com

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