When embedding python from C, and importing "ctypes" module in embedded 
script, it always crashes on Py_Finalize() on 4th cycle.
Tested with both PyRun_SimpleString(...) and PyRun_String(...).
Platform: Windows XP
IDE's: LabWindows/CVI 8.5 and Code::Blocks/gcc

Code:
--------------------------
#include <stdio.h>
#include <python.h>

int main()
{
    int i;
    for (i=0; i<10; i++)
    {
        printf("--- %d ---\n", i);
        Py_Initialize();
        PyRun_SimpleString("import ctypes");
        Py_Finalize();
    }
    return 0;
}
--------------------------------
Output:
--------------------------------
--- 0 ---
--- 1 ---
--- 2 ---
--- 3 ---

Process returned -1073741819 (0xC0000005)   execution time : 3.109 s
Press any key to continue.
--------------------------------

Tested
   obj=PyImport_ImportModule("ctypes");
   Py_DECREF(obj);
instead of PyRun_SimpleString(...) - same result

on python2.5 / mac os x 10.5.7:

$ cat main.c
#include <stdio.h>
#include <python.h>

int main()
{
    int i;
    for (i=0; i<10; i++)
    {
        printf("--- %d ---\n", i);
        Py_Initialize();
        PyRun_SimpleString("import ctypes");
        Py_Finalize();
    }
    return 0;
}

$ gcc -I/usr/include/python2.5/ -L/usr/lib/python2.5/ -lpython main.c
$ ./a.out 
--- 0 ---
--- 1 ---
--- 2 ---
--- 3 ---
Assertion failed: (type->tp_flags & Py_TPFLAGS_HEAPTYPE), function 
type_dealloc, file Objects/typeobject.c, line 2148.
Abort trap
$ uname -mprsv
Darwin 9.7.0 Darwin Kernel Version 9.7.0: Tue Mar 31 22:52:17 PDT 2009; 
root:xnu-1228.12.14~1/RELEASE_I386 i386 i386

I hope attached patch will fix this issue.