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Embedded Python and C Callback functions

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  Embedded Python and C Callback functions doc.mefisto@gmail.com - 2015-06-06 11:09 -0700
    Re: Embedded Python and C Callback functions dieter <dieter@handshake.de> - 2015-06-07 08:02 +0200
      Re: Embedded Python and C Callback functions doc.mefisto@gmail.com - 2015-06-07 01:37 -0700
      Re: Embedded Python and C Callback functions doc.mefisto@gmail.com - 2015-06-07 01:56 -0700
        Re: Embedded Python and C Callback functions Laura Creighton <lac@openend.se> - 2015-06-07 11:49 +0200
          Re: Embedded Python and C Callback functions doc.mefisto@gmail.com - 2015-06-07 02:51 -0700
        Re: Embedded Python and C Callback functions Stefan Behnel <stefan_ml@behnel.de> - 2015-06-07 22:32 +0200
      Re: Embedded Python and C Callback functions doc.mefisto@gmail.com - 2015-06-07 02:15 -0700
        Re: Embedded Python and C Callback functions dieter <dieter@handshake.de> - 2015-06-08 07:44 +0200

#92186 — Embedded Python and C Callback functions

Hi. I'm a newbie in python. But I want embed it in my C program.

There is such method of my class:
@staticmethod
def install_instr_callback(callback):
    # set hook for every change of PC
    m68k.set_instr_hook_callback(callback)

And in my C code there is such callback function:
static PyObject *my_instr_callback(PyObject *self);

I want call install_instr_callback from C with specifying of my callback. I do:
PyObject_CallMethod(myClass, "install_instr_callback", "(O)", my_instr_callback);
But python writes me: [b]null argument to internal routine[/b].

How can I fix this problem?

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#92204

doc.mefisto@gmail.com writes:

> Hi. I'm a newbie in python. But I want embed it in my C program.
>
> There is such method of my class:
> @staticmethod
> def install_instr_callback(callback):
>     # set hook for every change of PC
>     m68k.set_instr_hook_callback(callback)
>
> And in my C code there is such callback function:
> static PyObject *my_instr_callback(PyObject *self);
>
> I want call install_instr_callback from C with specifying of my callback. I do:
> PyObject_CallMethod(myClass, "install_instr_callback", "(O)", my_instr_callback);
> But python writes me: [b]null argument to internal routine[/b].

If this output really comes from "PyObject_CallMethod", then
some passed in argument is likely "null" - maybe "myclass"?

The Python-C interface is complicated. It might be advicible to
use e.g. "cython" to get the boilder plate code and some intricacies
taken care of. I have done this with "dm.xmlsec.binding". You
can find in its source also an example for the callback defined
in Python and called from "C".

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#92212

No, myclass is not null. I think my style of passing arguments is wrong.

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#92214

And I can't use Cython, because I have C++ module, and I have to use it.

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#92220

In a message of Sun, 07 Jun 2015 01:56:47 -0700, doc.mefisto@gmail.com writes:
>And I can't use Cython, because I have C++ module, and I have to use it.
>-- 
>https://mail.python.org/mailman/listinfo/python-list

Are you using Boost?
http://www.boost.org/doc/libs/1_58_0/libs/python/doc/

It handles lots of the setup for you.

Laura

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#92221

> >And I can't use Cython, because I have C++ module, and I have to use it.
> >-- 
> >https://mail.python.org/mailman/listinfo/python-list
> 
> Are you using Boost?
> http://www.boost.org/doc/libs/1_58_0/libs/python/doc/
> 
> It handles lots of the setup for you.
> 
> Laura

No, I'm not using Boost. Pure Python.h

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#92301

doc.mefisto@gmail.com schrieb am 07.06.2015 um 10:56:
> And I can't use Cython, because I have C++ module, and I have to use it.

That's not a valid reason. Cython supports C++ code just fine.

http://docs.cython.org/src/userguide/wrapping_CPlusPlus.html

Stefan

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#92216

I'm trying to debug and find my error. It goes wrong when:
 PyObject *v;
            v = va_arg(*p_va, PyObject *);
            if (v != NULL) {
                if (*(*p_format - 1) != 'N')
                    Py_INCREF(v);
            }

it tries to PyINCREF to my passed callback.

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#92327

doc.mefisto@gmail.com writes:

> I'm trying to debug and find my error. It goes wrong when:
>  PyObject *v;
>             v = va_arg(*p_va, PyObject *);
>             if (v != NULL) {
>                 if (*(*p_format - 1) != 'N')
>                     Py_INCREF(v);
>             }
>
> it tries to PyINCREF to my passed callback.

This indicates that it expects the "callback" to be a Python object.

Check the C-API specification. It should tell you which parameters
are expected to be Python objects and which C objects.

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