Function References

[squishywaffle]

Greetings,

I'm trying to wrap a function in a C library as a compiled C Python
module. Everything is going great, but I've hit a snag. There's a
function in the form of this:

First the typedef:
typedef void(*FPtr_Devi ceMessageHandle r) (const DeviceMessage, const
char*);

Then the actual function prototype:
FPtr_DeviceMess ageHandler
RegisterDeviceM essageHandler(F Ptr_DeviceMessa geHandler);

Whenever this USB device I'm using generates a message, it's then sent
to that function whose reference you passed to
RegisterDeviceM essageHandler() . Here's an example:

void testfunc() {
printf("test");
}
....on to main()
RegisterDeviceM essageHandler(& testfunc)

So I've defined a similar function on my C module to do just this,
using the passed function reference to allow the device to send
messages to a Python function of the user's choice. I'm just not sure
how to do this, and the tutorials I've been digging through don't
offer any help. I've found some functions that look promising, but
can't figure out how to cast the function reference from Python into
something the C RegisterDevice. .. function can handle. Here's what
I've got:

static PyObject *
Py1_RegisterDev iceMessageHandl er(PyObject *self, PyObject *args)
{
PyObject *handle, *parsed;

if(!PyArg_Parse Tuple(args, "O", handle)) {
return NULL;
}

parsed = PyMethod_Functi on(handle);
I1_RegisterDevi ceMessageHandle r(PyMethod_Func tion(handle));

Py_RETURN_TRUE;
} // end Py1_RegisterDev iceMessageHandl er()

This fails since PyMethod_Functi on returns a PyObject. Is there a way
to cast this to something generic? Casting to (void*) didn't seem to
work.

Thanks in advance!

[Diez B. Roggisch]

sq***********@g mail.com wrote:

Greetings,

I'm trying to wrap a function in a C library as a compiled C Python
module. Everything is going great, but I've hit a snag. There's a
function in the form of this:

First the typedef:
typedef void(*FPtr_Devi ceMessageHandle r) (const DeviceMessage, const
char*);

Then the actual function prototype:
FPtr_DeviceMess ageHandler
RegisterDeviceM essageHandler(F Ptr_DeviceMessa geHandler);

Whenever this USB device I'm using generates a message, it's then sent
to that function whose reference you passed to
RegisterDeviceM essageHandler() . Here's an example:

void testfunc() {
printf("test");
}
...on to main()
RegisterDeviceM essageHandler(& testfunc)

So I've defined a similar function on my C module to do just this,
using the passed function reference to allow the device to send
messages to a Python function of the user's choice. I'm just not sure
how to do this, and the tutorials I've been digging through don't
offer any help. I've found some functions that look promising, but
can't figure out how to cast the function reference from Python into
something the C RegisterDevice. .. function can handle. Here's what
I've got:

static PyObject *
Py1_RegisterDev iceMessageHandl er(PyObject *self, PyObject *args)
{
PyObject *handle, *parsed;

if(!PyArg_Parse Tuple(args, "O", handle)) {
return NULL;
}

parsed = PyMethod_Functi on(handle);
I1_RegisterDevi ceMessageHandle r(PyMethod_Func tion(handle));

Py_RETURN_TRUE;
} // end Py1_RegisterDev iceMessageHandl er()

This fails since PyMethod_Functi on returns a PyObject. Is there a way
to cast this to something generic? Casting to (void*) didn't seem to
work.

Thanks in advance!

May I suggest you move to ctypes for wrapping? It's easier, pure python and
callbacks are already built-in.

Diez

[squishywaffle]

Hello Diez.

May I suggest you move to ctypes for wrapping? It's easier, pure python and
callbacks are already built-in.

I'm pretty new to extending Python in C, I don't understand what
you're saying. Are there any examples or a brief explanation/URL you
could point me to?

[Diez B. Roggisch]

sq***********@g mail.com wrote:

Hello Diez.

>May I suggest you move to ctypes for wrapping? It's easier, pure python
and callbacks are already built-in.

I'm pretty new to extending Python in C, I don't understand what
you're saying. Are there any examples or a brief explanation/URL you
could point me to?

Is google dead today?

http://www.google.com/search?q=pytho...UTF-8&oe=UTF-8

First hit.

Ctypes is a since python2.5 built-in module that allows to declare
interfaces to C-libraries in pure python. You declare datatypes and
function prototypes, load a DLL/SO and then happily work with it. No C, no
compiler, no refcounts, no nothing.

And you can pass python-functions as callbacks.

See the module docs for examples.

Diez

[squishywaffle]

Ctypes is a since python2.5 built-in module that allows to declare

interfaces to C-libraries in pure python. You declare datatypes and
function prototypes, load a DLL/SO and then happily work with it. No C, no
compiler, no refcounts, no nothing.

And you can pass python-functions as callbacks.

The first sentence (and some really crummy licensing restrictions
imposed by the library distributor) alone here excludes this as a
valid option for this particular case, I definitely need Python 2.4
support.

So the question comes back around to being how is this same desired
behavior duplicated in the Python/C API?

[Diez B. Roggisch]

sq***********@g mail.com wrote:

>Ctypes is a since python2.5 built-in module that allows to declare
interfaces to C-libraries in pure python. You declare datatypes and
function prototypes, load a DLL/SO and then happily work with it. No C,
no compiler, no refcounts, no nothing.

And you can pass python-functions as callbacks.

The first sentence (and some really crummy licensing restrictions
imposed by the library distributor) alone here excludes this as a
valid option for this particular case, I definitely need Python 2.4
support.

How much more liberal can it get than MIT-licensed?

"""
to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
"""

But then, if you insist, go down the hard road.

Diez

[Diez B. Roggisch]

Diez B. Roggisch wrote:

sq***********@g mail.com wrote:

>>Ctypes is a since python2.5 built-in module that allows to declare
interfaces to C-libraries in pure python. You declare datatypes and
function prototypes, load a DLL/SO and then happily work with it. No C,
no compiler, no refcounts, no nothing.

And you can pass python-functions as callbacks.

The first sentence (and some really crummy licensing restrictions
imposed by the library distributor) alone here excludes this as a
valid option for this particular case, I definitely need Python 2.4
support.

How much more liberal can it get than MIT-licensed?

"""
to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
"""

Sorry, missed the paragraph

"""
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
"""

Still, AFAIK MIT is pretty liberal.

Diez

[squishywaffle]

How much more liberal can it get than MIT-licensed?

Again, the licensing issue is everything to do with the original
library distributor, NOT ctypes.

But then, if you insist, go down the hard road.

Irrelevant and unnecessary. If you don't want to help, don't please
don't reply.

[Diez B. Roggisch]

sq***********@g mail.com wrote:

>How much more liberal can it get than MIT-licensed?

Again, the licensing issue is everything to do with the original
library distributor, NOT ctypes.

I read library distributor as "ctypes-library distributor" because it is
3rd-party under 2.4. Which was the reason I quotet it's MIT-license.

And it escapes me what accessing the lib from ctypes is any different than
from your own compiled code.

>But then, if you insist, go down the hard road.

Irrelevant and unnecessary. If you don't want to help, don't please
don't reply.

I take the freedom to do so as I see fit - this is usenet...

Diez

[squishywaffle]

On Jul 31, 10:47*am, "Diez B. Roggisch" <de...@nospam.w eb.dewrote:

I take the freedom to do so as I see fit - this is usenet...

Fine, then keep beating a dead horse by replying to this thread with
things that do nobody any good. It seems like there are a lot better
way to waste time, though.

The Python/C API can get me back further without reliance on third-
party libraries than ctypes. It also isn't subject to the quirks that
ctypes is on platforms other than Windows (the target application runs
on Windows, Mac, and eventually Linux once the original distributor
has drivers for the device). I'm not even sure ctypes could load the
lib/driver the distributor packaged.

So really, I appreciate the option in ctypes, it's good stuff. But
it's not for this project.

Once again, the original question stands for anyone who has experience
with the Python/C API callbacks.