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Www.PySIGArcRiley22Jan2009r1.1 - 26 Jan 2009 - 11:34 - TedRochetopic end
The 22-January-2009 Python Special Interest Group (PySIG) hosted a meeting where %MAINWEB%.ArcRiley presented on developing extensions in C for Python 3.0. Notes follow, and source are included in the attachments at the bottom of the page.

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Building a Python 3.0 Extension
the missing PyModule_* functions

These functions (PyModule_*) are not included in the Python 3.0 documentation but their use can be derived from Python's source code.  See http://bugs.python.org/issue4614
which indicates this has been fixed and will be included in future releases.

PyObject*
PyModule_Create(struct PyModuleDef*);

   Allocates and returns a Python module object for the supplied PyModuleDef struct:
      static struct PyModuleDef example_Module = { 
        PyModuleDef_HEAD_INIT, 
        "example",                           /*m_name*/ 
        "Example's PyDoc",                   /*m_doc*/ 
        -1,                                  /*m_size*/ 
        example_Methods,                     /*m_methods*/ 
        NULL,                                /*m_reload*/ 
        NULL,                                /*m_traverse*/ 
        NULL,                                /*m_clear*/ 
        NULL                                 /*m_free*/ 
      };

   NULL will be returned when an exception was raised (ie, out of memory).


int
PyModule_AddObject(PyObject*, const char*, PyObject*); 
   
   First argument is the module object (from PyModule_Create), 
   Second argument is the name of the new object in the module's namespace,
   Third argument is a pointer to a PyTypeObject (cast as a PyObject*) of the new object.
   Returns 0 on success, -1 on failure (result of initfunc).


int
PyModule_AddIntConstant(PyObject*, const char*, long); 

   As PyModule_AddObject but the 3rd argument is the value of a new  int object.


int
PyModule_AddStringConstant(PyObject*, const char*, const char*); 

   As PyModule_AddObject but the 3rd argument is the value of a new str object.
Building a Python 3.0 Extension
bookmarks you will need

object members
http://docs.python.org/3.0/c-api/structures.html#PyMemberDef
Link object struct members directly to object attributes.

argument and keyword parsing
http://docs.python.org/3.0/c-api/arg.html
These are extremely convenient functions which parse arguments and/or keywords, test their type and value limits, and convert them into C types (char*, short, long, etc).

standard exceptions
http://docs.python.org/3.0/c-api/exceptions.html#standard-exceptions
Reference this table whenever you need to raise an builtin exception

glib reference manual
http://library.gnome.org/devel/glib/unstable/
Not Python-specific, Glib is an invaluable cross-platform “swiss army knife” library you'll find yourself using in every C-based project.  Especially useful for threaded extensions!


handy macros you'll use everywhere

Returning None
This replaces “Py_INCREF(Py_None); return Py_None;” everywhere you need to return None. 
  Py_RETURN_NONE


Returning True/False
Same as above but for Py_True and Py_False
  Py_RETURN_TRUE
  Py_RETURN_FALSE


Returning Special Floats
Same as above but for Py_NAN and Py_HUGE_VAL
  Py_RETURN_NAN
  Py_RETURN_INF(sign)


Release and Reacquire the GIL (Global Interpreter Lock)
Working with the GIL can be a pain, but this macro pair makes it a little simpler:
  Py_BEGIN_ALLOW_THREADS
    (nogil code here)
  Py_END_ALLOW_THREADS

-- %MAINWEB%.TedRoche - 26 Jan 2009
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