Re: [Sqlalchemy-tickets] [sqlalchemy] #2161: Py3k support for the C extension

[sqlalchemy <mi...@zz...>]

#2161: Py3k support for the C extension
-------------------------------+-------------------------------
      Reporter:  ged           |      Owner:  pjenvey
          Type:  enhancement   |     Status:  new
      Priority:  medium        |  Milestone:  0.9.xx
     Component:  cextensions   |   Severity:  major - 1-3 hours
    Resolution:                |   Keywords:
Progress State:  needs review  |
-------------------------------+-------------------------------

Comment (by claudiofreire):

 Replying to [comment:6 taavi]:
 > Regarding {{{PyObject_HEAD_INIT}}}, looking at Python-2.6.2 vs
 Python-3.2, both in {{{Include/object.h}}}, I can see why you'd make the
 change from {{{PyObject_HEAD_INIT(type), 0}}} to
 {{{PyVarObject_HEAD_INIT(type, 0)}}}. On Py2k they generate identical code
 to the compiler by definition:
 > {{{
 > #define PyVarObject_HEAD_INIT(type, size)     \
 >       PyObject_HEAD_INIT(type) size,
 > }}}
 >
 > And that's NOT the case in Py3k (things get wrapped in an extra set of
 curlies):
 > {{{
 > #define PyVarObject_HEAD_INIT(type, size)       \
 >     { PyObject_HEAD_INIT(type) size },
 > }}}
 >
 > If {{{PyVarObject_HEAD_INIT}}} is the right thing to use in Py3k, then
 we should also use it in Py2k.

 So, this is py3:

 {{{

 #ifdef Py_LIMITED_API
 typedef struct _typeobject PyTypeObject; /* opaque */
 #else
 typedef struct _typeobject {
     PyObject_VAR_HEAD
 }}}

 And this is py2

 {{{
 typedef struct _typeobject {
     PyObject_VAR_HEAD
 }}}

 In both cases, it's variable size. This is done for base classes, which
 are stored in tuple-fashion, after the type object's struct.

 So, the correct thing is indeed to use VAR.

--
Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2161#comment:24>
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