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How to transfer data structure or class from Python to C/C++?

Hi friends,

I am a newer of Python. I want to ask below question:

I have a C/C++ application and I want to use Python as its extension.
To do that, I have to transfer some data structure from C/C++
application to Python and get some data structure from Python to C/C++
application. I have researched Python document, but the example only
describes how to transfer some simple data, such as integer,char,
etc.

Could you please guide me to do that? or tell me some document to have
a research?

Thanks.
Oct 16 '08 #1
10 3465
Hongtian:
Could you please guide me to do that? or tell me some document to have
a research?
You can start googling for:
- SWIG
- Boost.Python
- SIP
- ctypes (built-in module)
- And more.

Bye,
bearophile
Oct 16 '08 #2
On Oct 15, 8:08*pm, Hongtian <hongtian.i...@ gmail.comwrote:
Hi friends,

I am a newer of Python. I want to ask below question:

I have a C/C++ application and I want to use Python as its extension.
To do that, I have to transfer some data structure from C/C++
application to Python and get some data structure from Python to C/C++
application. I have researched Python document, but the example only
describes how to transfer some simple data, such as integer,char,
etc.

Could you please guide me to do that? or tell me some document to have
a research?

Thanks.
Take this for what it's worth. If I understand correctly, you want
this:

struct info {
char* name;
char* address;
int age;
};

int main( ) {
info A, B;
python_run( "\
from urllib import urlget\n\
from mylib import populate_struct \n\
page= urlget( 'http://something' )\n\
populate_struct ( page, A )\n\
populate_struct ( page, B )\n" );
if( A.ageB.age ) {
something_in_C( );
}
return 0;
}

Am I on the right track? Do you have any questions so far?
Oct 16 '08 #3
Not exactly.

In my C/C++ application, I have following function or flow:

void func1(....)
{
call PyFunc(struct Tdemo, struct &Tdemo1);
}

I mean I want to invoke Python function 'PyFunc' and transfer a data
structure 'Tdemo' to this function. After some process in Python, I
want it return 'Tdemo1' back to the C/C++ application.

I research boost.python and think it is not a reasonable solution
because it make the C/C++ application too complex.

Thanks.

On Oct 16, 12:09*pm, "Aaron \"Castironpi \" Brady"
<castiro...@gma il.comwrote:
On Oct 15, 8:08*pm, Hongtian <hongtian.i...@ gmail.comwrote:
Hi friends,
I am a newer of Python. I want to ask below question:
I have a C/C++ application and I want to use Python as its extension.
To do that, I have to transfer some data structure from C/C++
application to Python and get some data structure from Python to C/C++
application. I have researched Python document, but the example only
describes how to transfer some simple data, such as integer,char,
etc.
Could you please guide me to do that? or tell me some document to have
a research?
Thanks.

Take this for what it's worth. *If I understand correctly, you want
this:

struct info {
* char* name;
* char* address;
* int age;

};

int main( ) {
* info A, B;
* python_run( "\
from urllib import urlget\n\
from mylib import populate_struct \n\
page= urlget( 'http://something')\n\
populate_struct ( page, A )\n\
populate_struct ( page, B )\n" );
* if( A.ageB.age ) {
* * something_in_C( );
* }
* return 0;

}

Am I on the right track? *Do you have any questions so far?
Oct 16 '08 #4
On Oct 16, 9:10*am, Hongtian <hongtian.i...@ gmail.comwrote:
Not exactly.

In my C/C++ application, I have following function or flow:

void func1(....)
{
* * call PyFunc(struct Tdemo, struct &Tdemo1);

}

I mean I want to invoke Python function 'PyFunc' and transfer a data
structure 'Tdemo' to this function. After some process in Python, I
want it return 'Tdemo1' back to the C/C++ application.

I research boost.python and think it is not a reasonable solution
because it make the C/C++ application too complex.

Thanks.
I am stumped. Here's what I have.

/C file:

typedef struct {
int a;
float b;
} TypeA;

static PyObject *
methA(PyObject *self, PyObject *args) {
TypeA a;
TypeA b;
PyObject* fun;
PyObject* res;
TypeA* pa;
TypeA* pb;

PyArg_ParseTupl e( args, "O", &fun );
a.a= 10;
a.b= 20.5;
b.a= 30;
b.b= 40.5;
printf( "%p %p\n", &a, &b );

pa= &a;
pb= &b;

res= PyObject_CallFu nction( fun, "II", &pa, &pb );
Py_DECREF( res );

return PyInt_FromLong( 0 );
}

/Py file:

import ng27ext

import ctypes as c
class TypeA( c.Structure ):
_fields_= [
( 'a', c.c_int ),
( 'b', c.c_float )
]

def exposed( obj1, obj2 ):
print 'in exposed'
print hex( obj1 ), hex( obj2 )
a= c.POINTER( TypeA ).from_address( obj1 )
print a
print a.contents

print ng27ext.methA( exposed )

/Output:

0021FD48 0021FD40
in exposed
0x21fd48 0x21fd40
<ctypes.LP_Type A object at 0x009FF350>
<__main__.Typ eA object at 0x009FF4E0>
0

Which is unexpected. The address on line 4 should be the contents of
'obj1', 0x21fd48, which it's not. I must not be using 'from_address'
properly.
Oct 16 '08 #5
On Oct 16, 9:10*am, Hongtian <hongtian.i...@ gmail.comwrote:
Not exactly.

In my C/C++ application, I have following function or flow:

void func1(....)
{
* * call PyFunc(struct Tdemo, struct &Tdemo1);

}

I mean I want to invoke Python function 'PyFunc' and transfer a data
structure 'Tdemo' to this function. After some process in Python, I
want it return 'Tdemo1' back to the C/C++ application.

I research boost.python and think it is not a reasonable solution
because it make the C/C++ application too complex.

Thanks.

On Oct 16, 12:09*pm, "Aaron \"Castironpi \" Brady"

<castiro...@gma il.comwrote:
On Oct 15, 8:08*pm, Hongtian <hongtian.i...@ gmail.comwrote:
Hi friends,
I am a newer of Python. I want to ask below question:
I have a C/C++ application and I want to use Python as its extension.
To do that, I have to transfer some data structure from C/C++
application to Python and get some data structure from Python to C/C++
application. I have researched Python document, but the example only
describes how to transfer some simple data, such as integer,char,
etc.
Could you please guide me to do that? or tell me some document to have
a research?
Thanks.
Did you have any luck?
Oct 17 '08 #6
On Oct 16, 9:10 am, Hongtian <hongtian.i...@ gmail.comwrote:
Not exactly.

In my C/C++ application, I have following function or flow:

void func1(....)
{
call PyFunc(struct Tdemo, struct &Tdemo1);

}

I mean I want to invoke Python function 'PyFunc' and transfer a data
structure 'Tdemo' to this function. After some process in Python, I
want it return 'Tdemo1' back to the C/C++ application.

I research boost.python and think it is not a reasonable solution
because it make the C/C++ application too complex.

Thanks.

On Oct 16, 12:09 pm, "Aaron \"Castironpi \" Brady"

<castiro...@gma il.comwrote:
On Oct 15, 8:08 pm, Hongtian <hongtian.i...@ gmail.comwrote:
Hi friends,
I am a newer of Python. I want to ask below question:
I have a C/C++ application and I want to use Python as its extension.
To do that, I have to transfer some data structure from C/C++
application to Python and get some data structure from Python to C/C++
application. I have researched Python document, but the example only
describes how to transfer some simple data, such as integer,char,
etc.
Could you please guide me to do that? or tell me some document to have
a research?
Thanks.
Did you have any luck?
Oct 17 '08 #7
On Oct 16, 9:10*am, Hongtian <hongtian.i...@ gmail.comwrote:
Not exactly.

In my C/C++ application, I have following function or flow:

void func1(....)
{
* * call PyFunc(struct Tdemo, struct &Tdemo1);

}

I mean I want to invoke Python function 'PyFunc' and transfer a data
structure 'Tdemo' to this function. After some process in Python, I
want it return 'Tdemo1' back to the C/C++ application.

I research boost.python and think it is not a reasonable solution
because it make the C/C++ application too complex.

Thanks.
snip

Solution produced here. Includes dirty kludge, which will welcome
correction.

/C file:

#include <Python.h>

typedef struct {
int a;
float b;
} TypeA;

static PyObject *
methA(PyObject *self, PyObject *args) {
TypeA a;
TypeA b;
PyObject* fun;
PyObject* res;

PyArg_ParseTupl e( args, "O", &fun );
a.a= 10;
a.b= 20.5;

res= PyObject_CallFu nction( fun, "II", &a, &b );

printf( "%i %f\n", b.a, b.b );
Py_DECREF( res );

return PyInt_FromLong( 0 );
}

static PyMethodDef module_methods[] = {
{"methA", methA, METH_VARARGS, "No doc"},
{NULL, NULL, 0, NULL} /* Sentinel */
};
#ifndef PyMODINIT_FUNC /* declarations for DLL import/export */
#define PyMODINIT_FUNC void
#endif
PyMODINIT_FUNC
initng27ext(voi d)
{
PyObject* m;
m = Py_InitModule3( "ng27ext", module_methods,
"Custom.");
if (m == NULL)
return;
}

/Py file:

import ng27ext

import ctypes as c
class TypeA( c.Structure ):
_fields_= [
( 'a', c.c_int ),
( 'b', c.c_float )
]

from _ctypes import _cast_addr
_data_cast= c.PYFUNCTYPE( c.py_object, c.c_void_p, c.py_object,
c.py_object)( _cast_addr ) #dirty kludge

def exposed( obj1, obj2 ):
cob1= _data_cast( obj1, None, c.POINTER( TypeA ) )
cob2= _data_cast( obj2, None, c.POINTER( TypeA ) )
print cob1.contents.a , cob1.contents.b
cob2.contents.a = c.c_int( 60 )
cob2.contents.b = c.c_float( 70.5 )
print cob2.contents.a , cob2.contents.b

print ng27ext.methA( exposed )

/Compile & link:

c:/programs/mingw/bin/gcc ng27ext.c -c -Ic:/programs/python25/include
c:/programs/mingw/bin/gcc -shared ng27ext.o -o ng27ext.pyd -Lc:/
programs/python25/libs -lpython25

/Output:

10 20.5
60 70.5
60 70.500000
0
Press any key to continue . . .

Oct 17 '08 #8
En Fri, 17 Oct 2008 20:03:44 -0300, Aaron "Castironpi " Brady
<ca********@gma il.comescribió:
On Oct 16, 9:10*am, Hongtian <hongtian.i...@ gmail.comwrote:
>Not exactly.

In my C/C++ application, I have following function or flow:

void func1(....)
{
* * call PyFunc(struct Tdemo, struct &Tdemo1);

}

I mean I want to invoke Python function 'PyFunc' and transfer a data
structure 'Tdemo' to this function. After some process in Python, I
want it return 'Tdemo1' back to the C/C++ application.

I research boost.python and think it is not a reasonable solution
because it make the C/C++ application too complex.

Thanks.
snip

Solution produced here. Includes dirty kludge, which will welcome
correction.

/C file:

#include <Python.h>

typedef struct {
int a;
float b;
} TypeA;

static PyObject *
methA(PyObject *self, PyObject *args) {
TypeA a;
TypeA b;
PyObject* fun;
PyObject* res;

PyArg_ParseTupl e( args, "O", &fun );
a.a= 10;
a.b= 20.5;

res= PyObject_CallFu nction( fun, "II", &a, &b );

printf( "%i %f\n", b.a, b.b );
Py_DECREF( res );

return PyInt_FromLong( 0 );
}

static PyMethodDef module_methods[] = {
{"methA", methA, METH_VARARGS, "No doc"},
{NULL, NULL, 0, NULL} /* Sentinel */
};
#ifndef PyMODINIT_FUNC /* declarations for DLL import/export */
#define PyMODINIT_FUNC void
#endif
PyMODINIT_FUNC
initng27ext(voi d)
{
PyObject* m;
m = Py_InitModule3( "ng27ext", module_methods,
"Custom.");
if (m == NULL)
return;
}

/Py file:

import ng27ext

import ctypes as c
class TypeA( c.Structure ):
_fields_= [
( 'a', c.c_int ),
( 'b', c.c_float )
]

from _ctypes import _cast_addr
_data_cast= c.PYFUNCTYPE( c.py_object, c.c_void_p, c.py_object,
c.py_object)( _cast_addr ) #dirty kludge

def exposed( obj1, obj2 ):
cob1= _data_cast( obj1, None, c.POINTER( TypeA ) )
cob2= _data_cast( obj2, None, c.POINTER( TypeA ) )
print cob1.contents.a , cob1.contents.b
cob2.contents.a = c.c_int( 60 )
cob2.contents.b = c.c_float( 70.5 )
print cob2.contents.a , cob2.contents.b

print ng27ext.methA( exposed )

/Compile & link:

c:/programs/mingw/bin/gcc ng27ext.c -c -Ic:/programs/python25/include
c:/programs/mingw/bin/gcc -shared ng27ext.o -o ng27ext.pyd -Lc:/
programs/python25/libs -lpython25

/Output:

10 20.5
60 70.5
60 70.500000
0
Press any key to continue . . .

--
http://mail.python.org/mailman/listinfo/python-list


--
Gabriel Genellina

Oct 21 '08 #9
On Oct 21, 12:46*am, "Gabriel Genellina" <gagsl-...@yahoo.com.a r>
wrote:
En Fri, 17 Oct 2008 20:03:44 -0300, Aaron "Castironpi " Brady *
<castiro...@gma il.comescribió:
On Oct 16, 9:10*am, Hongtian <hongtian.i...@ gmail.comwrote:
Not exactly.
In my C/C++ application, I have following function or flow:
void func1(....)
{
* * call PyFunc(struct Tdemo, struct &Tdemo1);
}
I mean I want to invoke Python function 'PyFunc' and transfer a data
structure 'Tdemo' to this function. After some process in Python, I
want it return 'Tdemo1' back to the C/C++ application.
I research boost.python and think it is not a reasonable solution
because it make the C/C++ application too complex.
Thanks.
snip
Solution produced here. *Includes dirty kludge, which will welcome
correction.
snip
>
--
Gabriel Genellina
Hi Gabriel,
Sorry, did you have some questions about it?
Oct 21 '08 #10

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