[C++-sig] How to expose to a python user defined type with to/from_python convertors?
How do I expose my C++ type to a user defined python type? I think I could use
boost python class_<> wrapper to wrap around, but if I want to use
to_python/from_python convertors?
Say I want to expose my C++ class(CA) to a python type(PA):
C++:
class CA
{
public:
//ctors, accessors...
private:
std::string name_;
int value_;
};
Python:
class PA(object):
def __init__(self, name, value):
self.name=name
self.value=value
If I use,
void initializeConverters()
{
using namespace boost::python;
to_python_converter();
}
with
struct CA_to_PA
{
static PyObject* convert(CA const& s)
{
printf("In C++ -> python converter?\n");
std::string name=s.name();
int value=s.value();
#if 0
static boost::python::object obj;
PyObject* obj_ptr=obj.ptr();
PyObject_SetAttrString(obj_ptr, "name",
PyString_FromString(name.c_str()));
PyObject_SetAttrString(obj_ptr, "value",
PyInt_FromLong(value));
return boost::python::incref(obj_ptr);
#else
return boost::python::incref(
//PyInt_FromLong(1999)
Py_BuildValue("s", "native string works")
//Py_BuildValue("{s:i,s:i}", "abc", 123, "def", 456)
);
#endif
}
};
How do I create a boost::python::object (or PyObject*) with "name" and "value"
attributes? I could get creation and return of python native types to work, but
can not get user defined types returned to the python side -- always get
NoneType returned.
boost::python::object C2Py()
{
printf("Pre assignment\n");
#if 0
boost::python::object obj(new CA("From C++ to python", 987654321));
PyObject* o=obj.ptr();
#else
CA a("From C++ to python", 987654321);
PyObject *o=CA_to_PA::convert(a);
#endif
printf("Post assignment\n");
PyObject *tmp=NULL;
std::string name="No Name";
int value=-1;
tmp=PyObject_GetAttrString(o, "name");
if (tmp!=NULL) name=PyString_AsString(tmp);
tmp=PyObject_GetAttrString(o, "value");
if (tmp!=NULL) value=PyInt_AsLong(tmp);
printf("(%s, %d)\n", name.c_str(), value);
return obj;
}
$ python
Python 2.5.1 (r251:54863, Oct 5 2007, 11:16:46)
[GCC 4.1.1 20070105 (Red Hat 4.1.1-53)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import mytypes
>>> pa=mytypes.C2Py()
("No Name", -1)
>>>type(pa)
NoneType
Any help is appreciated, thanks!
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Re: [C++-sig] How to expose to a python user defined type with to/from_python convertors?
> How do I expose my C++ type to a user
> defined python type? I think I could use boost python
> class_<> wrapper to wrap around, but if I want to use
> to_python/from_python convertors?
>
> Say I want to expose my C++ class(CA) to a python
> type(PA):
>
> C++:
> class CA
> {
> public:
> //ctors, accessors...
> private:
> std::string name_;
> int value_;
> };
>
> Python:
> class PA(object):
> def __init__(self, name, value):
> self.name=name
> self.value=value
>
> If I use,
>
> void initializeConverters()
> {
> using namespace boost::python;
> to_python_converter CA_to_pA>();
> }
>
> with
>
> struct CA_to_PA
> {
> static PyObject* convert(CA const&
> s)
> {
> printf("In C++ ->
> python converter?\n");
>
> std::string
> name=s.name();
> int
> value=s.value();
>
> #if 0
> static
> boost::python::object obj;
> PyObject*
> obj_ptr=obj.ptr();
>
>
> PyObject_SetAttrString(obj_ptr, "name",
>
> PyString_FromString(name.c_str()));
>
> PyObject_SetAttrString(obj_ptr, "value",
>
> PyInt_FromLong(value));
>
> return
> boost::python::incref(obj_ptr);
> #else
> return
> boost::python::incref(
>
> //PyInt_FromLong(1999)
>
> Py_BuildValue("s", "native string works")
>
> //Py_BuildValue("{s:i,s:i}", "abc", 123, "def", 456)
> );
> #endif
> }
> };
>
> How do I create a boost::python::object (or PyObject*) with
> "name" and "value" attributes? I could get creation and
> return of python native types to work, but can not get user
> defined types returned to the python side -- always get
> NoneType returned.
>
> boost::python::object C2Py()
> {
> printf("Pre assignment\n");
>
> #if 0
> boost::python::object obj(new CA("From
> C++ to python", 987654321));
> PyObject* o=obj.ptr();
> #else
> CA a("From C++ to python", 987654321);
> PyObject *o=CA_to_PA::convert(a);
> #endif
>
> printf("Post assignment\n");
>
> PyObject *tmp=NULL;
>
> std::string name="No Name";
> int value=-1;
>
> tmp=PyObject_GetAttrString(o, "name");
> if (tmp!=NULL)
> name=PyString_AsString(tmp);
>
> tmp=PyObject_GetAttrString(o, "value");
> if (tmp!=NULL) value=PyInt_AsLong(tmp);
>
> printf("(%s, %d)\n", name.c_str(),
> value);
>
> return obj;
> }
>
> $ python
> Python 2.5.1 (r251:54863, Oct 5 2007, 11:16:46)
> [GCC 4.1.1 20070105 (Red Hat 4.1.1-53)] on linux2
> Type "help", "copyright", "credits" or "license" for more
> information.
> >>> import mytypes
> >>> pa=mytypes.C2Py()
> ("No Name", -1)
> >>>type(pa)
> NoneType
>
> Any help is appreciated, thanks!
>
Any comments? Am I asking the right question? Basically I have a simple C++
type and want to extend it to python. However, I haven't figured out a way to
do the C++ to python conversion with boost python's to_python/from_python
converter scheme. Am I missing something?
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Re: [C++-sig] How to expose to a python user defined type with to/from_python convertors?
--- On Tue, 5/25/10, Michele De Stefano wrote: > From: Michele De Stefano > Subject: Re: [C++-sig] How to expose to a python user defined type with > to/from_python convertors? > To: "Development of Python/C++ integration" > Date: Tuesday, May 25, 2010, 10:52 AM > There's a very good tutorial on > writing from/to python converters. > This tutorial was suggested to me by one of the members of > this > mailing list and I've found it very useful. > > The link is this one: > http://misspent.wordpress.com/2009/09/27/how-to-write-boost-python-converters/ > > After reading this very useful article, I managed to write > my > mds-utils library (the link is at the end of this e-mail) > which you > can download to see how you can write a from/to python > converter. > > Bye. > Michele > It worked! Sorry for the late reply, I was tied up with a few other things... I just tested a bit and everything works now. I miseed the part where you need to import python type definitions into the C++ environment and somehow thought I could just add attributes on the fly. Thanks a lot! ___ Cplusplus-sig mailing list Cplusplus-sig@python.org http://mail.python.org/mailman/listinfo/cplusplus-sig
