Mailman 3 June 2004 - Cplusplus-sig

Calling a python function from C++.
by Jeff Holle June 29, 2004

June 29, 2004

I'm using boost 1_31_0 on Mandrake 10.0 Linux. I've created a simple demonstration of calling a python function with C++ object args using python.boost. It currently works with one exception. In the face of a missing python script, it "aborts" instead of properly throwing an exception if I use the "handle<>" machinery that boost.python offers. The following code fragment contains the working code with the stuff that should do the equivalent, but exibits this problem, commented out. PyObject * /* Returns a borrowed reference */ getPythonFunction(string moduleName,string functionName) { // handle<> _module( PyImport_ImportModule(const_cast<char *>(moduleName.c_str()))); // if ( _module.get() == NULL) throwException("The python module \"",moduleName.c_str(),"\" is not available",NULL); // handle<> _namespace(borrowed( PyModule_GetDict(_module.get()))); // if ( _namespace.get() == NULL) throwException("Failed to acquire the dictionary of \"",moduleName.c_str(),"\"",NULL); // handle<> _function(borrowed(PyDict_GetItemString( _namespace.get(),functionName.c_str()))); // if ( _function.get() == NULL) throwException("Failed to find needed function \"",functionName.c_str(),"\"",NULL); // return _function.get(); PyObject *pModule = PyImport_ImportModule(const_cast<char *>(moduleName.c_str())); if ( pModule == NULL) throwException("The python module \"",moduleName.c_str(),"\" is not available",NULL); PyObject *pDict = PyModule_GetDict(pModule); if ( pDict == NULL) throwException("Failed to acquire the dictionary of \"",moduleName.c_str(),"\"",NULL); PyObject *pFunc = PyDict_GetItemString(pDict,functionName.c_str()); if ( pFunc == NULL) throwException("Failed to find requested python function \"",functionName.c_str(),"\"",NULL); Py_DECREF(pModule); return pFunc; } In this form, this function throws a std::run_time exception which is successfully caught with a "catch (exception& x)" clause. With the commented out section active, something is thrown, but it can only be caught with "catch(...)". I'm wondering if anybody can explain this. I'm also wondering if I could contribute this example to boost.python. The python script that I call is: import sys from Greeter import * def AlterGreeting( greeting): greeting.setLanguage("Python") return greeting.greet() if __name__ == '__main__': print 'testing module' greetingObj = Greeter("C++") greeting = AlterGreeting(greetingObj) print greeting Note that the Greeter module is a C++ extension module also created with boost.python using pyste. The C++ part of this example does the same thing that the main module specific section of this python script does. If anybody wants this example, simple request it. I'll provide the complete project, which uses bjam v1, in a tar ball.

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Re: Calling a python function from C++.
by thor.arne.johansen＠ibas.no June 29, 2004

June 29, 2004

>In gmane.comp.python.c++, you wrote: >> I'm using boost 1_31_0 on Mandrake 10.0 Linux. >> >> I've created a simple demonstration of calling a python function with >> C++ object args using python.boost. >> It currently works with one exception. In the face of a missing python >> script, it "aborts" instead of properly throwing an exception if I use >> the "handle<>" machinery that boost.python offers. The following code >> fragment contains the working code with the stuff that should do the >> equivalent, but exibits this problem, commented out. > >Hi Jeff, > >I'd be interested to see your code. I am trying (not very successfully >so far) to figure out this stuff myself, and any working examples are >helpful. It sounds like you have a better handle on this stuff (no pun >intended) than I do. :-) > >Please email it to the my email address shown above. Thanks. > > Faheem. A while back I posted some example code for embedding python and have python 'scripts' manipulate C++ objects. It might also be of interest: http://mail.python.org/pipermail/c++-sig/2002-December/002833.html -- Thor Arne Johansen Dept. Manager R&D Ibas AS

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pyste, patch to allow injecting code in class definition
by Baptiste Lepilleur June 28, 2004

June 28, 2004

The attached patch allows the user to inject code in the class definition code, just like declaration_code() & module_code(). Among other things, this allows us to add properties when pyste support fail (anonymous union...). Example of usage: Vector3 = Class( "Ogre::Vector3", "OgreVector3.h" ) class_code( Vector3, '.def_readwrite( "x", &Ogre::Vector3::x )' ) class_code( Vector3, '.def_readwrite( "y", &Ogre::Vector3::y )' ) class_code( Vector3, '.def_readwrite( "z", &Ogre::Vector3::z )' ) Which produces: class_< Ogre::Vector3 >("Vector3", init< >()) .def(init< Ogre::Real, Ogre::Real, Ogre::Real >()) .def_readwrite( "x", &Ogre::Vector3::x ) .def_readwrite( "y", &Ogre::Vector3::y ) .def_readwrite( "z", &Ogre::Vector3::z ) ; Baptiste.

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calling python function from C++ using call
by Faheem Mitha June 27, 2004

June 27, 2004

Hi, I'm trying to call the function `array' (from the python module numarray.strings) from inside C++ code. This function initializes a character array. It has the arguments array(buffer=None, itemsize=None, shape=None, byteoffset=0, bytestride=None, kind=CharArray) I'm doing this as follows: The C++ end looks like **************************************************************** bcallback.cc **************************************************************** ... object charr(PyObject* func, list buf, object itemsize, tuple sh) { return boost::python::call<object>(func, buf, itemsize, sh); } ... **************************************************************** and the Python end looks like **************************************************************** callback.py **************************************************************** from bcallback import charr import numarray.strings as numstrings def retcharr(buffer, sh): return charr(numstrings.array, buffer, None, sh) **************************************************************** This actually works. Namely: In [2]: import callback In [3]: callback.retcharr(['a', 'c', 'a', 'c', 'a', 'c', 'g', 't', 'g','t','g','t'], (6,2)) Out[3]: CharArray([['a', 'c'], ['a', 'c'], ['a', 'c'], ['g', 't'], ['g', 't'], ['g', 't']]) However, I'm wondering if this is the best way of proceeding, or if there is a better way. Thanks in advance for comments. Faheem.

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Getter/Setter as Property with Pyste
by Achim Domma (Procoders) June 27, 2004

June 27, 2004

Hi, I try to generate Code with Pyste. The wrapped classes have lots of getter and setter functions. The generated code looks like this: .def("borderColor", (void (Magick::Image::*)(const Magick::Color&) )&Magick::Image::borderColor) .def("borderColor", (Magick::Color (Magick::Image::*)() const)&Magick::Image::borderColor) Is there a simple way to tell Pyste to generate an add_property call for 'borderColor' instead of the two functions? regards, Achim

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Pyste: wrapper function for overloaded function problems
by paul.bridger June 27, 2004

June 27, 2004

I am trying to expose a C++ member function with a bunch of default arguments, but I also want to provide a C++ wrapper for it. The problem I've had is that Pyste still generates the overload machinery even though it's not wanted since my wrapper function takes different arguments. Any hints? I'm going digging in the Pyste source. Paul Bridger

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Boost: multithreading initiated by a module
by Sasha Prikhod'ko June 26, 2004

June 26, 2004

Dear Python and Boost developers! I encountered a problem with threading in Visual Studio build. Thez a C++ project having in base some special Python site-library. A module start a thread, while a function is called from C++ project. But thread strangely dies at once! What is the reason? --- wrong build, wrong integration, wrong call... Moreover, I cannot certainly recocnize this trouble as serious and tie with plenty of threading discussions... :) Sincerely, Alex

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RE: [C++-sig] boost.python crush
by Max Khesin June 25, 2004

June 25, 2004

Thanks - my searching eventually yielded this: http://www.boost.org/libs/python/doc/building.html#variants with the appropriate VC6 instructions at the bottom. This took care of it. m. > -----Original Message----- > From: Ralf W. Grosse-Kunstleve [mailto:rwgk@yahoo.com] > Sent: Friday, June 25, 2004 10:12 AM > To: Development of Python/C++ integration > Subject: Re: [C++-sig] boost.python crush > > > Is this under Windows? If yes you have to be very careful how > you link. Certain > combinations of DLL's lead to obscure failures like yours. > There was a thread > about this recently; should be in the archieve: > > http://mail.python.org/pipermail/c++-sig/ > > Look for "windows", "dll", "debug". > If you are using a different platform post the exact details. > Ralf > > --- Max Khesin <MKhesin(a)liquidnet.com> wrote: > > I have the following sample class exposed via boost.python: > > > > class String > > { > > public: > > String(const std::string& v):m_val(v){} > > bool lessThan(const std::string& other) > const{return > > this->m_val<other;} > > bool greaterThan(const std::string& other) > const{return > > this->m_val>other;} > > bool equals(const std::string& other) > const{return > > this->m_val==other;} > > bool regexMatch(const std::string& other) > const{return > > this->m_val==other;} > > bool withinDistance(const std::string& other, int dist) > const{return > > distance(this->m_val, other)<=dist;} > > private: > > std::string m_val; > > }; > > > > > > BOOST_PYTHON_MODULE(test) > > { > > class_<String>("String", init<const std::string&>()) > > .def("lessThan", &String::lessThan) > > .def("greaterThan", &String::greaterThan) > > .def("equals", &String::equals) > > .def("regexMatch", &String::regexMatch) > > .def("withinDistance", &String::withinDistance) > > ; > > } > > > > I am calling this from python: > > > > >> import test > > >> s = test.String('hallo') > > >> s.lessThen('hello') #### <<< CRUSH > > > > the debugger seems to point to an access violation in > std::string dtor. I > > palyed around with making the argument a plain std::string > (instead of const > > std::string&) and const char* - both of those crush, albeit > in a different > > place (also dtors, from the looks of it) > > > > Any idea? > > > > thanks, > > > > max > > This email and any files transmitted with it are > confidential and intended > > solely for the use of the individual or entity to whom they > are addressed. If > > you have received this email in error please notify the > system manager. This > > message contains confidential information and is intended > only for the > > individual named. If you are not the named addressee you should not > > disseminate, distribute or copy this e-mail. > > > > _______________________________________________ > > C++-sig mailing list > > C++-sig(a)python.org > > http://mail.python.org/mailman/listinfo/c++-sig > > > > > > > __________________________________ > Do you Yahoo!? > New and Improved Yahoo! Mail - Send 10MB messages! > http://promotions.yahoo.com/new_mail > > _______________________________________________ > C++-sig mailing list > C++-sig(a)python.org > http://mail.python.org/mailman/listinfo/c++-sig > This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail.

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boost.python crush
by Max Khesin June 25, 2004

June 25, 2004

I have the following sample class exposed via boost.python: class String { public: String(const std::string& v):m_val(v){} bool lessThan(const std::string& other) const{return this->m_val<other;} bool greaterThan(const std::string& other) const{return this->m_val>other;} bool equals(const std::string& other) const{return this->m_val==other;} bool regexMatch(const std::string& other) const{return this->m_val==other;} bool withinDistance(const std::string& other, int dist) const{return distance(this->m_val, other)<=dist;} private: std::string m_val; }; BOOST_PYTHON_MODULE(test) { class_<String>("String", init<const std::string&>()) .def("lessThan", &String::lessThan) .def("greaterThan", &String::greaterThan) .def("equals", &String::equals) .def("regexMatch", &String::regexMatch) .def("withinDistance", &String::withinDistance) ; } I am calling this from python: >> import test >> s = test.String('hallo') >> s.lessThen('hello') #### <<< CRUSH the debugger seems to point to an access violation in std::string dtor. I palyed around with making the argument a plain std::string (instead of const std::string&) and const char* - both of those crush, albeit in a different place (also dtors, from the looks of it) Any idea? thanks, max This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail.

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Making Boost.Python understand DerivedSafe
by Chad Austin June 25, 2004

June 25, 2004

(I am not yet subscribed to the list... it seems mailman is having trouble sending me the authorization. Please CC me on replies.. Thanks.) Hi all, I just started using Boost.Python to embed Python in a project of mine. I spent a couple days evaluating, testing, and studying, but it seems to have paid off! Great job on making such a time-saving library! I am wrapping an internally refcounted class called CutScene. CutScene objects are referenced by RefPtr<CutScene> smart pointers, typedef'd as CutScenePtr. I export the class with: class_<CutScene, CutScenePtr>("CutScene").def /*etc*/; So far, so good. The problem comes about when I want to pass a CutScenePtr into object::operator() to call a function. If I pass a CutScenePtr object in, it says something about reject_raw_object_ptr: d:\Projects\empyrean\empyrean\third-party-vc7\include\boost\python\converter\arg_to_python.hpp(244) : error C2784: 'void boost::python::converter::detail::reject_raw_object_ptr(T *)' : could not deduce template argument for 'T1 *' from 'pyr::RefPtr<T>' with [ T=pyr::CutScene ] If I pass the result of CutScenePtr::get() into operator() I get a runtime error about Boost.Python not knowing how to convert RefDerivedSafe<T>* to a Python object. This makes sense, because RefPtr's implicit conversion operator, operator->, and get() all return RefDerivedSafe<T>*. (RefDerivedSafe<T> is a special class derived from T that prevents C++ clients from accidentally calling delete, ref(), or unref() on a smart pointer. This techique is used in both ATL and nsCOMPtr in Mozilla). Here's my question: Is there a way to tell Boost.Python that ptr(someCutScenePtr) is valid and should be equivalent to ptr(someCutScenePtr.get()) and/or that RefDerivedSafe<T>* can be implicitly converted to T*? I've tried several different things, and nothing seems to work... I'm currently using Boost 1.31 with both gcc 3.3.1 and VS.NET 2003. Many thanks, Chad

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