Unable to return a long integer from embedded Python to C++

Question

Hi I am trying to return a value (119599936) from the embedded python to C++

Py_Initialize();
PyObject* myModuleString = PyString_FromString((char*)"memory_leak_test");
PyObject* myModule = PyImport_Import(myModuleString);
PyObject* myFunction = PyObject_GetAttrString(myModule,(char*)"begin");
PyObject* args = PyTuple_Pack(1,PyString_FromString("CacheSetup"));
PyObject* myResult = PyObject_CallObject(myFunction, args);
double result = PyFloat_AsDouble(myResult);// <<<<<<<<< I guess thts where i'm goin wrong
std::cout << result << std::endl;
Py_Finalize();

I tried

unsigned long result = PyLong_AsUnsignedLong(myResult);
unsigned long long result = PyLong_AsUnsignedLongLongMask(myResult);
double result = PyLong_AsDouble(myResult2);

None of the above seemed to work for the when I try to return the number 119599936, the error i'm getting is

Exception SystemError: '..\\Objects\\longobject.c:739: bad argument to internal
function' in 'garbage collection' ignored
Fatal Python error: unexpected exception during garbage collection

user4815162342 · Accepted Answer · 2014-07-01 10:05:41Z

Since your code performs no error checking whatsoever, and you don't provide the source to the memory_leak_test module, it's anyone's guess what went wrong. My guess would be that memory_leak_test failed to import, or that memory_leak_test.begin("CacheSetup") raised an exception or returned None instead of returning a number like your code expects.

To debug this problem, rewrite with the following guidelines in mind:

Check errors from Python/C functions that may return them. Whenever an error you can't handle appears, call PyErr_Print() and terminate current execution (unless you are expecting the error and want to handle it properly - in that case, call PyErr_Clear() instead.)
Invoke Py_DECREF on objects returned as new references once you no longer need them. Examples of these are the return values of PyString_FromString, PyTuple_Pack, and PyObject_CallOject.
Learn of and use convenience functions such as PyObject_CallFunction, PyObject_CallMethod, and PyImport_ImportModule which significantly reduce boilerplate code for creating temporary strings and tuples. The best way to find these is by perusing existing Python/C sources, such as those that come with Python.
Use PyObject_Print() to print intermediate results for debugging.

Here is a possible modification of your code according to the above:

Py_Initialize();

PyObject *module = PyImport_ImportModule("memory_leak_test");
if (!module) {
  PyErr_Print();
  return;
}
PyObject *result = PyObject_CallMethod(module, "begin", "s", "CacheSetup");
Py_DECREF(module);
if (!result) {
  PyErr_Print();
  return;
}
printf("got result of type %s\n", Py_TYPE(result)->tp_name);
PyObject_Print(result, stdout, 0);
putchar('\n');

Py_DECREF(result);
Py_Finalize();

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