Thanks for examining and advise a solution. Before testing CPython I wanted to run this very simple think to send a tuple to a method of a python class.
I have succeeded in sending a tuple (declared exactly the same way as I do in the code) to a method written in a python file
but as soon as you put the method in a class and try to send a tuple it doesn't work(get a run failed message)
I don't send 3 arguments, it's a mistake from me to code that way,it leads to misunderstanding, it's 3 items in one tuple (declared args), 3 is just chosen by sample, it has to be dynamic later to send a series of data in a tuple.
I modifed the code and try to do this thing: (again it works when the method doesn't belong to a class and this what is very "strange" for me) and it's still doesn't work
// WE pass a tuple
pTuple = PyTuple_New(10);
if (pTuple == NULL) {
Py_DECREF(pTuple);
cout << "Can't build argument list for method call\n";
}
PyObject *py_argument;
for (int i = 0 ; i < 10 ; i++ ) {
py_argument = PyFloat_FromDouble(5.*(double)i);
PyTuple_SetItem(pTuple, i, py_argument);
}
args = Py_BuildValue("(O)", pTuple);
if (args == NULL) {
Py_DECREF(args);
error("Can't build argument list for class instance");
}
// Call our object method with arguments
ret = PyEval_CallObject(method,args);
---- Message d'origine ----
De : paspa...@noos.fr
À : python-list@python.org
Objet : C-API: Pass a tuple to a method of a class
Date : 10/01/2012 11:57:38 CET
Hello
I am trying to pass a tuple to a method of a class from C++ to Python. I get a Run Failed from the execution.
thanks for help/suggestions
the code is the following:
Python Code:
class cVector:
def __init__(self,msg):
self.value = msg
def ComputeNorm(self,vecData):
#don't use vecData for instance
result = 12.
return(result)
C++ Code :
//instances. farenheit will hold our return value
PyObject *ret, *mymod, *pclass, *method, *args, *object;
float retValue;
Py_Initialize();
//PySys_SetPath("/home/pascal/projPytCpp/proj1");
PySys_SetPath(".");
// Module
mymod = PyImport_ImportModule("mModule8");
if (mymod == NULL){
cout << "Can't Open a module:\n" ;
Py_DECREF(mymod);
}
// Class
pclass = PyObject_GetAttrString(mymod, "cVector");
if (pclass == NULL) {
Py_DECREF(pclass);
cout << "Can't find class\n";
}
// Parameters/Values
args = Py_BuildValue("(f)", 100.0);
if (args == NULL) {
Py_DECREF(args);
cout << "Can't build argument list for class instance\n";
}
// Object with parameter/value
object = PyEval_CallObject(pclass, args);
if (object == NULL) {
Py_DECREF(object);
cout << "Can't create object instance:\n";
}
// Decrement the argument counter as we'll be using this again
Py_DECREF(args);
// Get the object method - note we use the object as the object
// from which we access the attribute by name, not the class
method = PyObject_GetAttrString(object, "ComputeNorm");
if (method == NULL) {
Py_DECREF(method);
cout << "Can't find method\n";
}
// Decrement the counter for our object, since we now just need
// the method reference
Py_DECREF(object);
// Build our argument list - an empty tuple because there aren't
// any arguments
cout << "Prepare the Tuple:\n" ;
// WE pass a tuple
args = PyTuple_New( 3 );
if (args == NULL) {
Py_DECREF(args);
cout << "Can't build argument list for method call\n";
}
PyObject *py_argument;
// 1st argument
py_argument = PyFloat_FromDouble(5.);
PyTuple_SetItem(args, 0, py_argument);
// 2nd argument
py_argument = PyFloat_FromDouble(10.);
PyTuple_SetItem(args, 1, py_argument);
// 3nd argument
py_argument = PyFloat_FromDouble(15.);
PyTuple_SetItem(args, 2, py_argument);
cout << "Before the Exec:\n" ;
// Call our object method with arguments
//ret = PyEval_CallObject(method,args);
ret = PyObject_CallObject(method,args);
if (ret == NULL) {
Py_DECREF(ret);
cout << "Couldn't call method\n";
}
// Convert the return value back into a C variable and display it
PyArg_Parse(ret, "f", &retValue);
printf("Farenheit: %f\n", retValue);
// Kill the remaining objects we don't need
Py_DECREF(method);
Py_DECREF(ret);
// Close off the interpreter and terminate
Py_Finalize();
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