Visibility of symbols between extension modules

Sudharshan S sudharsh at gmail.com
Sun Oct 21 19:25:18 CEST 2007


Hi,

On Sun, 2007-10-21 at 13:43 -0300, Gabriel Genellina wrote:
> En Sun, 21 Oct 2007 08:21:50 -0300, Sudharshan S <sudharsh at gmail.com>  
> escribi�:
>
> What is foo? a directory? And bar/_foo/baz, source files in C? Each one  
> defining a module object, or is there a single module - foo perhaps?
> 

Sorry, let me explain things a bit, foo is a directory with an
__init__.py to tell the interpreter that foo is a package and bar, _foo,
baz are shared extension objects, with their sources as bar.c, _foo.c
and baz.c, each with its own PyMODINIT_FUNC function.

> Is it a global C variable, or a module attribute? If you want it to be  
> available to other Python code, it should be a module attribute. In this  
> case, you retrieve the value using PyObject_GetAttrString as with any  
> other object.
> If it's a global C variable, once it's assigned it should be visible to  
> all (but decades of warning against using global variables can't be  
> wrong...)
> The single most common error using the Python API is getting wrong the  
> reference counts. If you lose a reference, your object may be garbage  
> collected. If you leak a reference, it will never be freed. Maybe this is  
> what happens here.

Its not a module attribute, Just a good old C structure. I thought I
couldnt use Py_INCREF on non-PyObjects. After a gdb session, I found
that my variable say spam, is initialised when the _foo.so is loaded but
the moment baz.so or something get loaded, it becomes NULL again,
although its still in the current scope. (found that on my backtrace). I
hope I am right with the loading of .so part. Is that how python works,
bringing all the symbols in the different modules in a common
namespace?. If so why is spam losing its value. 

I also found that the interpreter calls init functions of all the
modules the moment I do a "import foo". I also suspect my setup script
is kinda doing something wrong. 

> Perhaps if you explain a bit more what you want to do someone can give  
> some advice.

Well, my code should tell everything. But a word of request, try not to
laugh at it. 
http://projects.openmoko.org/plugins/scmsvn/viewcvs.php/python-gsmd/?root=python-openmoko
It would be great if anyone could take a look and guide me out of this. 
The variable in question is "lgsmh" defined in _pygsmd.c.

I really feel I am missing something very trivial yet important thing.

Thanks for all the help..
-- 
Sudharshan S
http://www.sudharsh.wordpress.com




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