C Extension - return an array of longs or pointer?

[Java and Swing]

Hi,
I have been posting about writing a C extension for Python...so far,
so good. At least for the "simple" functions that I need to wrap.

Ok, my c function looks like...

MY_NUM *doNumberStuff(const char *in, const char *x) { ... }

MY_NUM is defined as, typedef unsigned long MY_NUM; (not sure if that
matters, or can i just create a wrapper which handles longs?)

anyhow..for my wrapper I have this..

static PyObject *wrap_doNumberStuff(PyObject *self, PyObject args) {
char *in = 0;
char *x = 0;
long *result = 0;
int ok = PyArg_ParseTuple(args, "ss", &in, &x);
if (!ok) return 0;

result = doNumberStuff(in, x);

return Py_BuildValue("l", result);
}

....my question is...in the c code, result is a pointer to an array of
longs, how can I get the returned result to be a list or something
similar to an array in Python?

....I also have a function which returns a character array (denoted by a
char *)...would it work the same as the previous question?

Thanks!!

[Brandon K]

All the veteran programmers out there can correct me, but the way I did
it in my extension was this:

static PyObject *wrap_doNumberStuff(PyObject* self, PyObject* args)
{
char* in = 0;
char* x = 0;
long* result = 0;
int i = 0;
PyObject* py = PyTuple_New()
int ok = PyArg_ParseTuple(args,"ss",&in, &x);
if(!ok) return NULL;

result = doNumberStuff(in,x):
len = sizeof(result)/sizeof(long)
for(i;i < len; i++)
PyTuple_SET_ITEM(py, i,Py_BuildValue("l",*result[i])
}

Simple enough idea...i'm not quite sure if I've done everything
correctly with the pointers, but I'm sure you can figure that out, the
algorithm is simple enough.

Hi,
I have been posting about writing a C extension for Python...so far,
so good. At least for the "simple" functions that I need to wrap.

Ok, my c function looks like...

MY_NUM *doNumberStuff(const char *in, const char *x) { ... }

MY_NUM is defined as, typedef unsigned long MY_NUM; (not sure if that
matters, or can i just create a wrapper which handles longs?)

anyhow..for my wrapper I have this..

static PyObject *wrap_doNumberStuff(PyObject *self, PyObject args) {
char *in = 0;
char *x = 0;
long *result = 0;
int ok = PyArg_ParseTuple(args, "ss", &in, &x);
if (!ok) return 0;

result = doNumberStuff(in, x);

return Py_BuildValue("l", result);
}

...my question is...in the c code, result is a pointer to an array of
longs, how can I get the returned result to be a list or something
similar to an array in Python?

...I also have a function which returns a character array (denoted by a
char *)...would it work the same as the previous question?

Thanks!!

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[Brandon K]

I'm sorry...I just woke up and forgot my C...must have left it in the
Coffee...Anyway, i made a few mistakes (can't initialize blank
tuple...function should return a value, lol).

static PyObject* wrap_doNumberStuff(PyObject* self, PyObject* args)
{
char* in = 0;
char* x = 0;
long* result = 0;
int i = 0;
PyObject* py = NULL;
if(!PyArg_ParseTuple(args,"ss",&in,&x) return NULL;

result = doNumberStuff(in,x);
len = sizeof(result)/sizeof(long);
py = PyTuple_New(len);
for(i; i < len; i++)
PyTuple_SET_ITEM(py, i, Py_BuildValue("l",*result[i]);

return py;
}

Additionally, the Python/C api in the docs tells you all of these nifty
little abstract layer functions that you can call from your extension.

All the veteran programmers out there can correct me, but the way I did
it in my extension was this:

static PyObject *wrap_doNumberStuff(PyObject* self, PyObject* args)
{
char* in = 0;
char* x = 0;
long* result = 0;
int i = 0;
PyObject* py = PyTuple_New()
int ok = PyArg_ParseTuple(args,"ss",&in, &x);
if(!ok) return NULL;

result = doNumberStuff(in,x):
len = sizeof(result)/sizeof(long)
for(i;i < len; i++)
PyTuple_SET_ITEM(py, i,Py_BuildValue("l",*result[i])
}

Simple enough idea...i'm not quite sure if I've done everything
correctly with the pointers, but I'm sure you can figure that out, the
algorithm is simple enough.

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[Java and Swing]

Interesting...thanks. Any good tutorials out there, other than the
python doc for ext?
thanks.

Brandon K wrote:

All the veteran programmers out there can correct me, but the way I did
it in my extension was this:

static PyObject *wrap_doNumberStuff(PyObject* self, PyObject* args)
{
char* in = 0;
char* x = 0;
long* result = 0;
int i = 0;
PyObject* py = PyTuple_New()
int ok = PyArg_ParseTuple(args,"ss",&in, &x);
if(!ok) return NULL;

result = doNumberStuff(in,x):
len = sizeof(result)/sizeof(long)
for(i;i < len; i++)
PyTuple_SET_ITEM(py, i,Py_BuildValue("l",*result[i])
}

Simple enough idea...i'm not quite sure if I've done everything
correctly with the pointers, but I'm sure you can figure that out, the
algorithm is simple enough.

Hi,
I have been posting about writing a C extension for Python...so far,
so good. At least for the "simple" functions that I need to wrap.

Ok, my c function looks like...

MY_NUM *doNumberStuff(const char *in, const char *x) { ... }

MY_NUM is defined as, typedef unsigned long MY_NUM; (not sure if that
matters, or can i just create a wrapper which handles longs?)

anyhow..for my wrapper I have this..

static PyObject *wrap_doNumberStuff(PyObject *self, PyObject args) {
char *in = 0;
char *x = 0;
long *result = 0;
int ok = PyArg_ParseTuple(args, "ss", &in, &x);
if (!ok) return 0;

result = doNumberStuff(in, x);

return Py_BuildValue("l", result);
}

...my question is...in the c code, result is a pointer to an array of
longs, how can I get the returned result to be a list or something
similar to an array in Python?

...I also have a function which returns a character array (denoted by a
char *)...would it work the same as the previous question?

Thanks!!

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[Bernhard Herzog]

Brandon K <pr***********@yahoo.com> writes:

long* result = 0; [...] result = doNumberStuff(in,x);
len = sizeof(result)/sizeof(long);

I don't think this will do what you appear to expect it to do.

Bernhard

--
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Skencil http://skencil.org/
Thuban http://thuban.intevation.org/

[Jorgen Grahn]

On 12 Oct 2005 04:46:34 -0700, Java and Swing <co*******@gmail.com> wrote:
....

...my question is...in the c code, result is a pointer to an array of
longs, how can I get the returned result to be a list or something
similar to an array in Python?
RTFM. There are API functions to create an empty list [] and to append
objects to a list. PyList_something(), I think.
...I also have a function which returns a character array (denoted by a
char *)...would it work the same as the previous question?

You might want to return this as a Python string, even if it's just random
octet data garbage. Depends on what that data really represents, but it's a
common idiom, and modules like struct and array expect their data to be
strings. Note that Python strings may contain NUL bytes.

/Jorgen

--
// Jorgen Grahn <jgrahn@ Ph'nglui mglw'nafh Cthulhu
\X/ algonet.se> R'lyeh wgah'nagl fhtagn!

[Martin v. Löwis]

Brandon K wrote:

PyTuple_SET_ITEM(py, i, Py_BuildValue("l",*result[i]);

Using Py_BuildValue is overkill here. PyInt_FromLong will do just
as well.

Regards,
Martin