On 12/11/2008, at 1:55 AM, Philipp Heuser wrote:

Hi all,

I am just starting to use the C API for Python. What I want to do is
to use an external funtion availabele in C and therfore I want to
'convert' a list of floats from Python to an array of floats in C
which I can forward to the external function. So first step is tp
parse a list to C and let the C code print the variables! The
obviously too simplistic approach is below... When I call this
function from python, e.g. cpp([1,2,3]) the output is: 25180552 25180540 25180528

Could you be so kind to help me here to get started with using C- functions from Python? Where is the error?

Thank you very much and kind regards,

Philipp

static PyObject * cpp_foo(PyObject *self, PyObject* args) { PyObject* obj; PyObject* seq; int i, len; if(!PyArg_ParseTuple(args, "O", &obj)) return NULL; seq = PySequence_Fast(obj, "expected a sequence"); len = PySequence_Size(obj); PyObject* item; int a;

for (i=0; i<len; i++) { item=PySequence_Fast_GET_ITEM(seq, i); a=item; // ?????????????????????????????????????????

Perhaps something like:

 long a;
 a = PyInt_AsLong(item);
 if (a == -1 && PyErr_Occurred())
     return NULL; /* error */
 printf("%i\n", a);

Cheers, Chris Miles

On Tue, Nov 11, 2008 at 12:55 PM, Philipp Heuser <philipp@achtziger.de> wrote:

Hi all,

I am just starting to use the C API for Python. What I want to do is to use an external funtion availabele in C and therfore I want to 'convert' a list of floats from Python to an array of floats in C which I can forward to the external function. So first step is tp parse a list to C and let the C code print the variables! The obviously too simplistic approach is below... When I call this function from python, e.g. cpp([1,2,3]) the output is: 25180552 25180540 25180528

Could you be so kind to help me here to get started with using C-functions from Python? Where is the error?

Thank you very much and kind regards,

Philipp

static PyObject * cpp_foo(PyObject *self, PyObject* args) { PyObject* obj; PyObject* seq; int i, len; if(!PyArg_ParseTuple(args, "O", &obj)) return NULL; seq = PySequence_Fast(obj, "expected a sequence"); len = PySequence_Size(obj); PyObject* item; int a;

for (i=0; i<len; i++) { item=PySequence_Fast_GET_ITEM(seq, i); a=item; // ?????????????????????????????????????????

Add more '?'s here. PySequence_FAST_GET_ITEM returns a PyObject, you can't just go and give it to 'a' to turn it into an integer. Also, this variable 'i' better be of type Py_ssize_t instead of int.

So, to get your value as a long, first check item is indeed a long using PyLong_Check(item) and then convert it to a long with PyLong_AsLong(item):

  printf("%i\n", a);

} Py_DECREF(seq); return None; }

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