Mailman 3 August 2006 - Cplusplus-sig

Wrapping shared_ptr of virtual classes
by Will Lee Aug. 9, 2006

Aug. 9, 2006

I have seen this post ( http://aspn.activestate.com/ASPN/Mail/Message/cpp-sig/2262721) a while a go but I couldn't find the response that solves this problem. Essentially, I couldn't find a way to wrap an abstract class that is being returned as a shared_ptr. For the following scenario: class A has virtual method f class B inherits from A that implements f class F that has a static method: shared_ptr<A> getInstance() Essentially I want to call F.getInstance().f() in python, which will call B::f All the documentation points to creating a wrapper class, so I have done so: struct AWrapper : A, wrapper<A> (would wrap function "f" that uses this->get_override() call to call the overridden function) My question is, like what is in the post, how do I declare class A? I don't think I can declare the AWrapper, since F.getInstance() returns shared_ptr<A> and not shared_ptr<AWrapper>: class_<AWrapper, shared_ptr<AWrapper>, boost::noncopyable>... I don't think I can declare with A either, since how can I tie the wrapper function calls? class_<A, shared_ptr<A>, boost::noncopyable> Then this just gets me confused in what it would do (I got a convert error saying that there is no to_python converter found): class_<A, AWrapper, shared_ptr<A>, boost::noncopyable> ... Your help is greatly appreciated. Will

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Calling list.__len__() from C++ causes crash with >= 100 elements
by Geoffrey French Aug. 8, 2006

Aug. 8, 2006

I tried to code the smallest module to demonstrate the problem. I presented it as a module so that people could get it working and running easily, to aid any debugging that might have been done. Sorry if I got the balance between too much code and too little, somewhat off. Regards Geoffrey French "Geoffrey French" <gsculpt at googlemail.com<http://mail.python.org/mailman/listinfo/c++-sig>> > writes: > > >* Here is the code for a C++ module to demonstrate this:* > > > ** > <snip> > > >* Is this a boost::python bug, or have I screwed up some how?* > >* Thank you for your time.* > > What is the *smallest* code that demonstrates it? > > -- > Dave Abrahams > Boost Consulting > www.boost-consulting.com

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Can Boost.Python help me?
by Qun Cao Aug. 8, 2006

Aug. 8, 2006

Hi Everyone, I am a beginner on cross language development. My problem at hand is to build a python interface for a C++ application built on top of a 3D game engine. The purpose of this python interface is providing a convenient scripting toolkit for the application. One example is that a user can write a python script like: player = Player() game.loadPlayer(player) player.moveTo(location) To configure the game environment. I am trying to figure out how to make this happen. I only have the vague idea that this concerns embedding/extending python with C++, but after reading Python Doc, SWIG, BOOST.Python, I am still not sure how to architecture it. Since the main program is still going to be the C++ application, I guess we need to embedding the python scripts in the C++ code. So at initialization stage, the python script needs to be loaded into the C++ code. And this code can be simple, like player = Player() game.loadPlayer(player) But for this to work, the python code needs to know the Player class, is it right? Does that mean I need to build a python wrapper class for Player and "import Player" in the python code? But because this application is built on top of a game engine, Player class inherits many classes from there, I cannot possibly wrapping them all, right? Also, some global objects are probably needed in this code of adding players, how can the python code access them? I know I probably don't have a grasp of basics here, please kindly enlighten me! Btw, if you can point me to any source code of non-trivial projects utilizing Boost.Python, that would be very helpful. I found the examples on the tutorials are far too simple. Thank you very much, Qun Cao

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boost.python version that contains indexing suite.
by Balasubramanyam, Shivakumar Aug. 8, 2006

Aug. 8, 2006

Hi, Can someone provide a tar file for the boost.python code that contains the indexing_suite_v2. The last time I tried, I had the compilation failures and could go no further. I followed the steps listed in http://home.clara.net/raoulgough/boost/index.html, but with the latest version of boost. cvs -z3 -d:pserver:anonymous@boost.cvs.sourceforge.net:/cvsroot/boost co -P boost cvs update -d -r indexing_v2 boost/python/suite/indexing cvs update -d -r indexing_v2 libs/python Any ideas? Thanks, Shiva

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Problem exposing templates
by Balasubramanyam, Shivakumar Aug. 8, 2006

Aug. 8, 2006

Hi, I have installed the latest cvs version of gccxml, pyplusplus, pygccxml I am attaching the code to this mail that has the problem. Files: Stack.h: Has the class template BP_Stack.cpp Contains the boost.python code generated by py++ Sconstruct-lib: Builds the stack library Sconstruct: Builds the boost-python-stack library <<genCode.py>> <<sconstruct>> <<sconstruct-lib>> <<Stack.h>> <<BP_Stack.cpp>> The compilation fails at line number 29 and 40. The problem the functional definition generated with "_GLOBAL__I_Stack.h****** { //::_GLOBAL__D_Stack.hLZJ4nd typedef void ( *function_ptr_t )( ); bp::def( "_GLOBAL__D_Stack.hLZJ4nd" , function_ptr_t( &::_GLOBAL__D_Stack.hLZJ4nd ) , bp::default_call_policies() ); } { //::_GLOBAL__I_Stack.hLZJ4nd typedef void ( *function_ptr_t )( ); bp::def( "_GLOBAL__I_Stack.hLZJ4nd" , function_ptr_t( &::_GLOBAL__I_Stack.hLZJ4nd ) , bp::default_call_policies() ); } Is there any ways else to explicitly instantiate the template? The class compiles and runs fine if I remove those two declarations. Thanks, Shiva

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STL list data member.
by Balasubramanyam, Shivakumar Aug. 8, 2006

Aug. 8, 2006

Hi, I have some classes which has std::list as public data members that need to be exposed. What is the good way to do it? The short term solution I can think of is to add a wrapper getter/setter method to convert to/from boost::python::list. I could probably use the decl_string from py++ to check if the member_data is "::std::list" and automate the wrapper generation. Does anyone else have other solutions? Thanks, Shiva

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Boost.Python: Caching Python object instances
by Doug Gregor Aug. 7, 2006

Aug. 7, 2006

Hello, I am using Boost.Python to expose the Boost Graph Library in Python. The vertices in the graph types are small structures that are always passed by value. A vertex looks something like this: struct Vertex { int index; Graph* graph; }; This class is exposed to python in the normal way: class_<vertex_descriptor>(); Now, each time that we convert a Vertex from C++ to Python, Boost.Python will create a new PyObject for it. This behavior has surprised us a few times, and contributes to some performance problems. So, I would like to cache the PyObject instances in the Graph object itself: class Graph { public: std::vector<boost::python::object> py_vertices; }; When I add a new vertex, I want to create a Python object for it and store that object in the py_vertices vector. Then, when Boost.Python needs to convert a vertex_descriptor value "v" to a Python object, I'd like to return "py_vertices[v.index]" instead of creating a new object. With lots of hackery, I've attained some limited success in this area. My approach is to register a to_python_vertex for the vertex type with this function object: struct cached_vertex_object { static PyObject* convert(const Vertex& v) { PyObject* result = v.graph->py_vertices[v.index].ptr(); Py_INCREF(result); return result; } }; to_python_converter<Vertex, cached_vertex_object>(); Of course, now I have the problem of creating the boost::python::object values to put in the cache! Digging around in the source a bit, I came up with this: typedef class_cref_wrapper<Vertex, make_instance<Vertex, value_holder<Vertex> > > Converter; Vertex result(this->py_vertices.size(), this); boost::python::object vertex_object(handle<>(Converter::convert (result))); this->py_vertices.push_back(result); This actually does work, but I get a sharp rebuke from Boost.Python whenever my extension module gets loaded: /u/dgregor/lib/python/boost/graph/__init__.py:10: RuntimeWarning: to- Python converter for boost::graph::python::basic_descriptor<void*, boost::undirectedS> already registered; second conversion method ignored. from _graph import * I have two questions: 1) Is there a better way to cache Python object instances with Boost.Python? 2) I've filtered out those Boost.Python warnings: will they come back to bite me eventually? Cheers, Doug

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[boost.python] void ptr problem
by michael_gruner＠arcor.de Aug. 7, 2006

Aug. 7, 2006

Hello, I'm trying to use boost.python to wrap a C function that takes a pointer on a void pointer as an argument. But I'm going wrong to use the example from the FAQ. Could anyone help me on this? my code looks like this: struct void_; BOOST_PYTHON_OPAQUE_SPECIALIZED_TYPE_ID(void_); int myfunc(char * mychar, void ** mypointer); int myfunc_wrp(char * mychar, void_ ** mypointer){ return myfunc(mychar,(void ** ) mypointer); } ... BOOST_PYTHON_MODULE(mymodule){ def("myfunc", &myfunc_wrp); } later in python I do: import mymodule mystring = " " mypointerobject = 0 mymodule.myfunc(mystring,mypointerobject) and get: Boost.Python.ArgumentError: Python argument types in mymodule.myfunc(str, int) did not match C++ signature: myfunc(char *, struct void_ * *) Are there any advices to solve this problem? thank you for your answers. Kind regards, Michael

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boost python compiling question.
by chun ping wang Aug. 6, 2006

Aug. 6, 2006

Hmm k i have a simple question, how would I build boost.python given this following information. I am using dev-cpp and its install in "c:\dev-cpp" folder. IN it contains the mingw32 sub directory My project folder is "c:\cs classes\cs386\c++". In it contains FiniteAutomta.cpp which maps to python module... my boost folder is "C:\boost_1_33_1" in it contains the bjam.exe file. PYTHON_ROOT = "C:\python24" Thanks for the help. I look at the tutorial but is confused on how I can build my project.

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boost.org broken link to this list
by Jorge Vargas Aug. 6, 2006

Aug. 6, 2006

Hello I'm new here and I was looking for boost support when I find out their link is broken. http://www.boost.org/more/mailing_lists.htm#projects broken link - http://www.python.org/community/sigs/c++-sig/ new link - http://www.python.org/community/sigs/current/c++-sig/

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