Tuple size and memory allocation for embedded Python

Steve Holden steve at holdenweb.com
Fri Jan 21 17:20:54 EST 2005

Jinming Xu wrote:

> Hi Folks,
> Python seems unstable, when allocating big memory.  For example, the 
> following C++ code creates a tuple of tuples:
>  PyObject* arCoord = PyTuple_New(n);
>  double d = 1.5;
>  for(int i=0; i<n; i++)
>    {
>      PyObject* coord = PyTuple_New(2);
>      PyTuple_SetItem(coord,0, PyFloat_FromDouble(d));//x
>      PyTuple_SetItem(coord,1, PyFloat_FromDouble(d));//y
>      PyTuple_SetItem(arCoord,i, coord);
>    }
> When the n is small, say 100, the code works fine.  when n is big, say 
> 10,000, Python has trouble allocating memory, saying:
> "Exception exceptions.IndexError: 'tuple index out of range' in 'garbage 
> collection' ignored
> Fatal Python error: unexpected exception during garbage collection
> Aborted"
> Could anyone please give me some insight or a fix for this?
> Thanks in advance for your answer.
I'm going to guess that the problem is related to incorrect reference 
counts. I don't see any IncRefs in there. It seems probable that the 
program will work until you make n high enough to trigger a garbage 
collection sweep, then memory your program still regards as allocated is 
garbage collected by Python and reused. Ugly :-P

Python is pretty stable, so it's usually best to suspect our own code 
unless you're heavily into using the C API (which I'm not, so feel free 
to ignore me).

Steve Holden               http://www.holdenweb.com/
Python Web Programming  http://pydish.holdenweb.com/
Holden Web LLC      +1 703 861 4237  +1 800 494 3119

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