Mailman 3 March 2007 - Cplusplus-sig

Py++ | Exposing Templates
by Anand, Kumar March 28, 2007

March 28, 2007

I am currently using version 0.8.2 of Py++. Is their support for exposing templates (basically template instantiations) automatically to python? I have the following code, and when I run it through Py++, compilation goes fine but I don't see the template instantiation being exposed. ---------- #include "ProtoA.h" //This defines a simple class called ProtoA #include "ProtocolStub.h" //This defines the template class:: template <class TYPE> class ProtocolStub : public TYPE { ...} inline void instantiate(){ sizeof( ProtocolStub<ProtoA> ); } typedef ProtocolStub < ProtoA > ProtoAStub; --------- Thanks Kumar

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Foo to FooWrapper
by Piotr Jaroszynski March 27, 2007

March 27, 2007

Hello, I suppose the code will show my problem better then myself, so: http://dev.gentooexperimental.org/~peper/boost/test.cc $ g++ -fPIC -shared -lboost_python -I/usr/include/python2.4 test.cc -o test.so and in python: >>> import test >>> test.getFoo().blah() 0 >>> test.getFoo().blah1() Traceback (most recent call last): File "<stdin>", line 1, in ? Boost.Python.ArgumentError: Python argument types in Foo.blah1(Foo) did not match C++ signature: blah1(FooWrapper {lvalue}) How can I fix that? Making a copy-ctor for Foo is a no option. I thought about using shared_ptr<Foo> copy-ctor but how? -- Best Regards, Piotr Jaroszynski

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Transfering ownership from python to C++
by Shawn McGrath March 26, 2007

March 26, 2007

Hi guys, I've been working on this problem for at least a week now, and I can't find a solution. I'm pretty much ready to give up this project if I can't fix this. In C++ I have a base class called Entity with two pure virtual functions: update and process which are exposed to python. I subclass Entity in python, and pass instances of the subclassed entities to a C++ function called "addEntity" defined like this: void pyAddEntity(const std::string &name, PyObject *e) { pyEntity *ent = boost::python::extract<pyEntity *>(e); assert(ent != NULL); EntityID eid = Engine::Instance().addEntity(ent, name); try { ent->self = e; ent->added = true; Py_XINCREF(ent->self); } catch (...) { handleError(); LOG("ERROR PY_XINCREF"); } } To kill the memory, I call pyEntity::kill() which sets a done flag to true, and the Engine deletes it. I tried putting Py_XDECREF(self) inside pyEntity's dtor and it crashes with the stacktrace showing ntdll, (so meaningless). I tried delaying the call to Py_XDECREF until after the gc has run, still no good. There's nothing I can do to call Py_XDECREF(). The delayed delete stacktrace is a little more meaningful, it shows (unknown frames removed): #1 007C34B0 std::auto_ptr<rsblsb::python::pyEntity>::~auto_ptr(this=0xabdeee8) (C:/MinGW/bin/../lib/gcc/mingw32/3.4.2/../../../../include/c++/3.4.2/memory:258) #2 006E126B boost::python::objects::pointer_holder<std::auto_ptr<rsblsb::python::pyEntity>, rsblsb::python::pyEntity>::~pointer_holder(this=0xabdeee0) (C:/Game/svn/Platform/Framework/Python/Modules/PyModuleEntity.cc:127) #3 600CD32E boost_python-mgw-1_33_1!_ZN5boost6python15instance_holder10deallocateEP7_objectPv() (C:\Game\svn\Platform\Output\boost_python-mgw-1_33_1.dll:??) #4 1E0AB496 python24!PyType_GenericNew() (C:\WINDOWS\system32\python24.dll:??) #10 0053945B rsblsb::python::InterpreterClass::process(this=0x5356f44d) (C:/Game/svn/Platform/Framework/Python/PythonInterpreter.cc:92) #17 6011E19C boost_python-mgw-1_33_1!_ZNK5boost6python6detail12wrapper_base12get_overrideEPKcP11_typeobject() (C:\Game\svn\Platform\Output\boost_python-mgw-1_33_1.dll:??) I tried changing the addEntity() function like so: void pyAddEntity(const std::string &name, std::auto_ptr<pyEntity> e); But that doesn't allow for virtual functions to be defined in Python, so that's not an option. Is there anything else I can try? I *REALLY* don't want to give up on this project, but I can't handle these memory leaks. Thanks a lot for the help -Shawn.

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Release Python's lock before destructing pointer_holder
by Gabriel Becedillas March 24, 2007

March 24, 2007

I'm wrapping a class whose destructor does some work on sockets that might take some time to complete, so I need to release Python's lock before calling the destructor. This instances are held via boost::shared_ptr. One way I could manage to do so is to declare a destructor for pointer_holder<> like this: pointer_holder::~pointer_holder() { PyThreadState* prev = PyThreadState_Swap(NULL); PyEval_ReleaseLock(); m_p = Pointer(); PyEval_AcquireLock(); PyThreadState_Swap(prev); } There are 2 reasons why I don't like this solution. The first one is that I have to modify boost::python's code. The second is that I need this only for a certain class. Does anyone know a better/cleaner way to do this ? Thanks. -- Gabriel Becedillas Developer CORE SECURITY TECHNOLOGIES

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Launch msvc debugger via bjam
by John Reid March 23, 2007

March 23, 2007

Hi, I have the following test in my Jamfile.v2 bpl-test gapped_pssm_test : test_gapped_pssm.py _gapped_pssms ; _gapped_pssms is the name of a python extension. I would like to launch python through my VC Express debugger. On the command line the following works: "C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\VCExpress" /debugexe python test_gapped_pssm.py How can I do this using bjam? The --debugger option and -sPYTHON_LAUNCH options that I have seen in various FAQs don't seem to work. I.e. the test is just run using python to launch it. Thanks, John.

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Duplicate registration of to-Python converters
by Pertti Kellomäki March 23, 2007

March 23, 2007

We are developing a system that allows user-written plugins. Some of these plugins can be written in Python, and they can access the internals of the system via bindings developed using Boost.Python. The plugins don't know anything about each other, so a plugin running Python calls Py_Initialize(), runs the Python code, and calls Py_Finalize(). The call to Py_Finalize() does not remove the registered to-Python converters, however, so if two plugins happen to import the same module produced by Boost.Python, the second importing causes RuntimeWarnings to be printed. Is there a way to turn these warnings off, remove the converters, or otherwise circumvent the problem? TIA. -- Pertti

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ownership of C++ object extended in Python
by Mark Williams March 22, 2007

March 22, 2007

In the Python FAQ Wiki at http://wiki.python.org/moin/boost.python/HowTo I see a heading titled "ownership of C++ object extended in Python" which discusses how to keep a PyObject* alive while the object it represents still exists in C++. It suggests writing a wrapper as follows: class MyClassWrap : public MyClass { MyClassWrap( PyObject* self_) : self(self_) { PyINCREF(self); } MyClassWrap( PyObject* self_, const MyClass& copy ) : MyClass(copy), self(self_) { PyINCREF(self); } ~MyClassWrap() { PyDECREF(self); } ... PyObject *self; }; I'm guessing (probably incorrectly) that this was written before the introduction of boost::python::wrapper<>. What I'd like to do is something like.. class MyClassWrap : public MyClass, wrapper<MyClass> { MyClassWrap() { Py_INCREF( detail::wrapper_base_::get_owner(*this) ) } ~MyClassWrap() { Py_DECREF( detail::wrapper_base_::get_owner(*this) ) } /* ... wrapped methods here ... */ } class_< MyClass, boost::intrusive_ptr<MyClass>, boost::noncopyable>("MyClass"); .. but of course get_owner returns 0 from within MyClassWrap() What is the correct way of incrementing/decrementing the reference count for the underlying PyObject* when using wrapper<>, please? Thanks in advance, Mark

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shared_ptr< const T> patch
by Roman Yakovenko March 20, 2007

March 20, 2007

Good evening. Few month ago I created patch to boost::shared_ptr< const T> problem. You can find full thread here: http://mail.python.org/pipermail/c++-sig/2006-November/011626.html The patch was approved by David Abrahams, but for some reason it was not applied. Could it be applied now? Thanks -- Roman Yakovenko C++ Python language binding http://www.language-binding.net/

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Problems with an instance of a Python class
by Pertti Kellomäki March 20, 2007

March 20, 2007

I am having troubles using an instance of a Python class. The offending code is below. I can create the instance and call its method without problems, but when the scope ends, I get a segmentation fault with the stack trace #0 PyErr_Fetch #1 PyInstance_NewRaw #2 ~object_base #3 ~object If I comment out the instance creation and calling the method of the instance, there are no problems, so it seems that the problem is in instance's destructor. I'm assuming it is something simple that I am overlooking, which causes reference counting to go haywire. Any ideas? Pertti ------------------------------------------- { Py_Initialize(); // Run Python file defining PythonSchedulerClass FILE *fp = fopen(pythonFile_.c_str(), "r"); PyRun_SimpleFileEx(fp, pythonFile_.c_str(), 1); // Retrieve the main module object main_module(( handle<>(boost::python::borrowed( PyImport_AddModule("__main__"))))); // Get the class object passClass(main_module.attr("PythonSchedulerPass")); // Create an instance object instance(passClass()); // Call a method of the obejct needsTarget_ = call_method<bool>(instance.ptr(), "needsTarget"); Py_Finalize(); // Crash here in ~object() } --------------------------------------------

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Trouble exposing a class function that returns std::vector<>
by Shawn McGrath March 20, 2007

March 20, 2007

I have a type defined in my existing C++ code as follows: typedef std::vector<RenderableThing *> RenderObjectList; and a class with a member function as follows: class GraphicObject { public: //... inline RenderObjectList &getRenderObjectList() { return render_object_list; } //... }; The vector type is exposed to python via: boost::python::class_<graphics::RenderObjectList >("RenderObjectList") .def(boost::python::vector_indexing_suite<graphics::RenderObjectList >()); How can I expose GraphicObject::getRenderObjectList() to python? I tried: .def("getRenderObjectList", &graphics::GraphicObject::getRenderObjectList) which gives error: error: no matching function for call to `boost::python::class_<rsblsb::graphics::GraphicObject, boost::python::detail::not_specified, boost::python::detail::not_specified, boost::python::detail::not_specified>::def(const char[20], <unknown type>)' I tried .def("getRenderObjectList", &graphics::GraphicObject::getRenderObjectList, boost::python::return_internal_reference<>()) which gives error: error: no matching function for call to `boost::python::class_<rsblsb::graphics::GraphicObject, boost::python::detail::not_specified, boost::python::detail::not_specified, boost::python::detail::not_specified>::def(const char[20], <unknown type>, boost::python::return_internal_reference<1u, boost::python::default_call_policies>)' I'm sure I just have to set the correct call policy, but I don't know the syntax, can anyone help? Thanks a lot, Shawn.

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