Mailman 3 October 2007 - Cplusplus-sig

CMake and getting starting with boost.python
by Braddock Gaskill Aug. 5, 2011

Aug. 5, 2011

Yesterday I became a boost.python user, after years of heavy SWIG usage. I would have started using boost.python years ago except for the bjam learning curve. I spent hours TRYING on multiple occasions, but got lost every time trying to get the page one example to build with bjam. Here is how to build the "greet" example with a four line CMake file: cat >>CMakeLists.txt <<EOF LINK_LIBRARIES(boost_python) INCLUDE_DIRECTORIES("/usr/include/python2.5") LINK_DIRECTORIES("/usr/lib/python2.5") # Not needed? ADD_LIBRARY(hello SHARED hello.cpp) EOF You WILL have to `mv libhello.so hello.so` after building. Works for me under Ubuntu Linux 6.10 after apt-get install cmake python2.5-dev boost-python-dev cmake make mv libhello.so hello.so ipython In [1]: import hello In [2]: hello.greet() Out[2]: 'hello, world' Boost.Python has been a joy to learn and use since I got past bjam. I had a moderately large API wrapped in just my first couple hours of learning (less time than I spent messing with bjam). Any additional advice for using CMake to build boost.python? Braddock Gaskill

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How to import a boost::python dll in windows?
by ichijoji Aug. 5, 2011

Aug. 5, 2011

I'm trying to port some research code that uses boost::python to expose a library to python to windows, but I'm having trouble importing the dll into python. I'm compiling using msvc 2005 and using python 2.5, but when I try to import the module I get this: Traceback (most recent call last): File "main.py", line 1, in <module> import object File "c:\code\sge\code\scripts\object.py", line 1, in <module> import sge ImportError: No module named sge My module is named sge and I'm compiling to sge.dll. Is there some obvious reason why python wouldn't be able to find my dll? When I compile on linux into an so this code works fine. -- View this message in context: http://www.nabble.com/How-to-import-a-boost%3A%3Apython-dll-in-windows--tf3… Sent from the Python - c++-sig mailing list archive at Nabble.com.

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Base class defined in other header file not included in bp::bases<>
by Haridev, Meghana Sept. 14, 2008

Sept. 14, 2008

Hi Folks, I'm having some trouble generating boost-python wrapper code using pyplusplus for a derived class which has one of its base classes defined in another file. Simple scenario: mydir/ other.hpp: class baseB{ }; hierarchy.hpp: #include "other.hpp" class baseA{ }; class derivedC: public baseA, public baseB{ }; generate_code.py: import os from pyplusplus import module_builder mb = module_builder.module_builder_t( files=['hierarchy.hpp'] ) mb.build_code_creator( module_name='inherit' ) mb.code_creator.user_defined_directories.append( os.path.abspath('.') ) mb.write_module('boost_hierarchy.cpp') ------------------------------------------------------------------------ ------------------------------------------------- Generated code (boost_hierarchy.cpp) looks like this: // This file has been generated by pyplusplus. #include "boost/python.hpp" #include "hierarchy.hpp" namespace bp = boost::python; BOOST_PYTHON_MODULE(inherit){ bp::class_< baseA >( "baseA" ); bp::class_< derivedC, bp::bases< baseA > >( "derivedC" ); } How can I get pyplusplus to add 'baseB' to bp::bases<> for 'derivedC' class when 'baseB' class is defined in another file (present in the same directory or different directory)? When I move the definition of 'baseB' class to hierarchy.hpp, boost wrapper for 'derivedC' is correctly generated as: bp::class_< derivedC, bp::bases< baseA, baseB > >( "derivedC" ); Thanks, -Meghana.

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Raoul Gough's container suite with svn boost-trunk boost.python?
by John Reid May 18, 2008

May 18, 2008

Has anyone tried using Raoul's container suite with the svn boost-trunk? I'm getting the following error: C:\Dev\ThirdParty\boost\boost-trunk\boost/python/detail/caller.hpp(236) : error C2903: 'extract_return_type' : symbol is neither a class template nor a function template C:\Dev\ThirdParty\boost\boost-trunk\boost/python/detail/caller.hpp(232) : while compiling class template member function 'boost::python::detail::py_func_sig_info boost::python::detail::caller_arity<2>::impl<F,Policies,Sig>::signature(void)' with [ F=boost::python::list (__cdecl *)(std::vector<biopsy::binding_hit> &,boost::python::indexing::slice), Policies=boost::python::indexing::detail::postcall_override<boost::python::indexing::default_container_policies>, Sig=boost::mpl::vector3<boost::python::list,std::vector<biopsy::binding_hit> &,boost::python::indexing::slice> ] So the problem seems to be there is no extract_return_type in boost::python::indexing::detail::postcall_override<boost::python::indexing::default_container_policies> If I remember correctly, I've installed Roman's version by copying it into boost/python/suite/indexing John.

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'iteritems', 'iterkeys' and 'itervalues' in dict
by Nindi Singh April 11, 2008

April 11, 2008

Apolgies for not putting the subject line in my last email. In the Boost.Python dict class there are methods 'iteritems', 'iterkeys' and 'itervalues' all returning objects. How exactly are you supposed to use these objects (iterators) ? ___________________________________________________________ Inbox full of spam? Get leading spam protection and 1GB storage with All New Yahoo! Mail. http://uk.docs.yahoo.com/nowyoucan.html

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Custom smart pointer with same behaviour as shared_ptr
by Francis Moreau Jan. 23, 2008

Jan. 23, 2008

Hi, I am passing Python objects to C++ through a shared_ptr smart pointer and it's work well. However I need to have the same behaviour as shared_ptr but with my own version of smart pointer. I try to register and expose my custom smart pointer but I have this compilation error: boost/python/pointee.hpp(28) : error C2039: 'element_type': is not a member of 'CountedObjPtr<T>' with [ T=PyCallEngineState ] boost/python/pointee.hpp(38) : see reference to class template instantiation 'boost::python::detail::pointee_impl<false>::apply<T>' being compiled with [ T=CountedObjPtr<PyCallEngineState> ] boost/python/register_ptr_to_python.hpp(17) : see reference to class template instantiation 'boost::python::pointee<T>' being compiled with [ T=CountedObjPtr<PyCallEngineState> ] PythonModules.cpp(113) : see reference to function template instantiation 'void boost::python::register_ptr_to_python<CountedObjPtr<T>>(void)'being compiled with [ T=PyCallEngineState ] Here is the content of the from_python file for my smart pointer: template <class T> struct CountedObjPtr_from_python { CountedObjPtr_from_python() { converter::registry::insert(&convertible, &construct, type_id<CountedObjPtr<T> >()); } static void* convertible(PyObject* p) { if (p == Py_None) { return p; } return converter::get_lvalue_from_python( p, python::converter::registered<T>::converters); } static void construct(PyObject* source, python::converter::rvalue_from_python_stage1_data* data) { void* const storage = ((python::converter::rvalue_from_python_storage<CountedObjPtr<T> >*)data)->storage.bytes; // Deal with the "None" case. if (data->convertible == source) { new (storage) CountedObjPtr<T>(); } else { new (storage) CountedObjPtr<T>(static_cast<T*>(data->convertible)); } data->convertible = storage; } }; And here is the code where I register the smart pointer: namespace boost{ namespace python{ template <class T> struct pointee< CountedObjPtr<const T> > { typedef T type; }; template <class T> inline T* get_pointer(CountedObjPtr<const T> const& p) { return const_cast<T*>(p.get()); } }} template <typename T> void register_CountedObjPtr_conversions() { boost::python::converter::registry::insert( &CountedObjPtr_from_python<T>::convertible, &CountedObjPtr_from_python<T>::construct, boost::python::type_id<CountedObjPtr<T> >()); } BOOST_PYTHON_MODULE(CallEngineExtending) { python::class_<PyCallEngineState, PyCallEngineState_Wrapped, boost::noncopyable>("PyCallEngineState") ; //register_ptr_to_python<boost::shared_ptr<PyCallEngineState> >(); python::register_ptr_to_python<CountedObjPtr<PyCallEngineState> >(); register_CountedObjPtr_conversions<PyCallEngineState>(); } Is anyone knows what is missing or wrong with this code? Also, I am not sure this code manages the ref counting properly since there is no call to borrowed or something like this? Any help would be appreciated, Francis

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std::tr1::shared_ptr as boost::shared_ptr
by Piotr Jaroszynski Jan. 16, 2008

Jan. 16, 2008

Hello, I am exposing a C++ app, which makes heavy use of tr1::shared_ptr, which seems to be exactly(?) the same as boost::shared_ptr. I have managed to make most of the stuff work just as it would be boost::shared_ptr ( additionally adding support for shared_ptr<const T> - thanks to [1] ): namespace my_app_namespace { //Make Boost.Python work with std::tr1::shared_ptr<> template<typename T_> inline T_ * get_pointer(std::tr1::shared_ptr<T_> const & p) { return p.get(); } //Make Boost.Python work with std::tr1::shared_ptr<const> template<typename T_> inline T_ * get_pointer(std::tr1::shared_ptr<const T_> const & p) { return const_cast<T_*>(p.get()); } } namespace boost { namespace python { //Make Boost.Python work with std::tr1::shared_ptr<> template<typename T_> struct pointee<std::tr1::shared_ptr<T_> > { typedef T_ type; }; //Make Boost.Python work with std::tr1::shared_ptr<const> template<typename T_> struct pointee<std::tr1::shared_ptr<const T_> > { typedef T_ type; }; } } What is still not working is the implicit conversion of Foo and Derived for functions taking std::tr1::shared_ptr<Foo>. With boost::shared_ptr it just works when you add the bp::bases<Foo> to the Derived: func(boost::shared_ptr<Foo>) ... bp::class_<Foo> ... bp::class_<Derived, bp::bases<Foo> > ... and func can take both Foo and Derived. But with std::tr1::shared_ptr I have to use: func(std::tr1::shared_ptr<Foo>) ... bp::class_<Foo, std::tr1::shared_ptr<Foo> > ... bp::class_<Derived, std::tr1::shared_ptr<Derived>, bp::bases<Foo> > ... bp::implicitly_convertible<std::tr1::shared_ptr<Foo>, std::tr1::shared_ptr<Derived> >(); How can I make it working just as with boost::shared_ptr? Btw. I have seen [2] already, but it doesn't seem to cover that. [1] - http://language-binding.net/pyplusplus/troubleshooting_guide/shared_ptr/sha… [2] - http://language-binding.net/pyplusplus/troubleshooting_guide/smart_ptrs/sma… -- Best Regards, Piotr Jaroszynski

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Am I crazy or is it my computer?
by Matthew Scouten Nov. 4, 2007

Nov. 4, 2007

This is diving me nuts. I need to triple check an assumption. I am *extending* python using Boost::Python, by wrapping a complex c++ library that was written years ago with no thought of future use in python. The library works by a system of callouts and callbacks with extensive multithreading. There are a number of minor worker threads in the background, but [ASSUMPTION ONE:] this should not matter because they never need to use data or call code that is known to the interpretor. There is also a callback thread on which the callbacks are called. This is NOT a python thread, an interpretor thread, or ANY other special kind of thread. It was not started through the C/Python API. It is a system thread started through the WIN32 API in the byzantine depths of the library. It has not been introduced to the interpretor in any way. ASSUMPTION TWO: I can have that thread call into python code by using the PyGILState_Ensure & PyGILState_Release pair of functions as described in http://www.python.org/dev/peps/pep-0311/ and http://docs.python.org/api/threads.html to acquire the Global Interpretor Lock. (Actually: I am using Resource Acquisition Is Initialization idiom with the following simple class: class callback { public: inline callback() { state = PyGILState_Ensure(); } inline ~callback() { PyGILState_Release(state); } private: PyGILState_STATE state; }; This may be ASSUMPTION THREE) Are my assumptions valid? This may seem like a simple question that I should be googling for, but like I said I am triple checking some assumptions. I have been trying to debug the same extremely bizarre problem for a couple of days now and it only shows up in the asynchronous callbacks.

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failed in PyImport_Import()
by Shrikant Chikhalkar Nov. 1, 2007

Nov. 1, 2007

Hi, i am tring to call python function from 'C' program. i get NULL value return by PyImport_Import() following is the code. code is copied from http://www.codeproject.com/cpp/embedpython_1.asp following file is saved as call_function.c /************************************************************************************************************/ // call_function.c - A sample of calling // python functions from C code // #include <Python.h> int main(int argc, char *argv[]) { PyObject *pName, *pModule, *pDict, *pFunc, *pValue; if (argc < 3) { printf("Usage: exe_name python_source function_name\n"); return 1; } // Initialize the Python Interpreter Py_Initialize(); // Build the name object pName = PyString_FromString(argv[1]); // Load the module object pModule = PyImport_Import(pName); // pDict is a borrowed reference pDict = PyModule_GetDict(pModule); // pFunc is also a borrowed reference pFunc = PyDict_GetItemString(pDict, argv[2]); if (PyCallable_Check(pFunc)) { PyObject_CallObject(pFunc, NULL); } else { PyErr_Print(); } // Clean up Py_DECREF(pModule); Py_DECREF(pName); // Finish the Python Interpreter Py_Finalize(); return 0; } /************************************************************************************************************/ python file saved as py_function.py /************************************************************************************************************/ '''py_function.py - Python source designed to ''' '''demonstrate the use of python embedding''' def multiply(): c = 12345*6789 print 'The result of 12345 x 6789 :', c return c /************************************************************************************************************/ $gcc -g call_function.c -lpython2.5 -ocall_function $./call_function py_function.py multiply i get following output ImportError: No module named py_function Failed to load "py_function" when i kdbg(debug) it i vet NULL value returned from PyImport_Import().. can any one please find out the error that i am doing. -- Shrikant

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Re: [C++-sig] Am I crazy or is it my computer?
by Ralf W. Grosse-Kunstleve Nov. 1, 2007

Nov. 1, 2007

I don't know too much about threading, but I think - you still need Niall Douglas' patches if your threads want to call back into Python - it is fair to say that the real problem is "Python & threading", mainly because of the dreaded global interpreter lock (GIL) Recently there has been some discussion on python-dev about getting rid of the GIL, but I'm not holding my breath... IIUC, if your threads never call back into Python you don't have to deal with the GIL. If you have to deal with the GIL I'm not surprised to see you frustrated. This is something that was largely ignored in the Boost.Python development (there is only so much you can hope to achieve in a given amount of time...). In my work I've consciously avoided threading. Under this simplification I find Boost.Python well documented and intuitive :-) Ralf ----- Original Message ---- From: Matthew Scouten <matthew.scouten(a)gmail.com> To: Development of Python/C++ integration <C++-sig(a)python.org> Sent: Wednesday, October 31, 2007 1:11:27 PM Subject: Re: [C++-sig] Am I crazy or is it my computer? Ok, I just found this: http://www.boost.org/libs/python/doc/v2/faq.html#threadsupport I seems to be saying that I can not do what I want with out patching Boost::Python (or does this only apply to multiple interpretors? ) Is this still true (please tell me it's been fixed)? if so, where can I get this patch and how do I apply it? I asked about multi-threading and boost python in on this list a while ago, and got no answer. I took this a a "go ahead, no problems". If I am being an idiot, could you tell me so? Just flame away at me so I know I've been stupid. A lot of people here actually know what they are doing. I do not have that luxury. I am finding boost python extremely complex and non-intuitive. There is also a lack of good documentation (example code is nice to have, but does not constitute proper documentation all by itself).

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