Mailman 3 September 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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'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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C++ singleton
by Emmanuel Taurel Oct. 31, 2007

Oct. 31, 2007

Hello everybody, I am actually writing an interface to python for an existing C++ library using Boost. This library has a C++ singleton class. This class has only one constructor (with arguments) which is "protected" because it's a singleton. I am not able to build a Boost interface to this class because the compiler complains that the constructor I have given to Boost in the class_xxx constructor argument is not public (which is true) ! Therefore, my question is simple : How is it possible to interface such a class with only one constructor which is protected and a static method to create/access the object ? Thank's very much for your answer. Sincerely Emmanuel Taurel (etaurel(a)cells.es) PS : By the way, is there a searchable archive of this mailing list ?

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How about class_<...>.enable_copy() ?
by Hans Meine Oct. 30, 2007

Oct. 30, 2007

Hi! I often use copy.[deep]copy() to copy python objects / BPL-exported types. This works if pickling support has been explicitly coded, by pickling and unpickling. It would be neat if there was an .enable_copy() or sth. like that, which would define a __copy__ (or __deepcopy__) method that simply calls the copy constructor. That would be more efficient than the pickling approach, both at runtime and in terms of saved LOCs. Have you thought about such a thing? Is there a common short idiom that does that already? Is there a rationale for not providing copying support? -- Ciao, / / /--/ / / ANS

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Re: [C++-sig] Announcing pybindgen
by Gustavo Carneiro Oct. 1, 2007

Oct. 1, 2007

(manually replying from copy-pasting the archives because my c++-sig subscription was disabled by accident). Nat Goodspeed wrote: >Gustavo Carneiro wrote: >> Hello all, >> >> I'd like to announce a new project for producing python extensions, >> called PyBindGen. It follows a radical new path for Python bindings >> generation: it is itself written in (gasp!) Python! And it does not >> even use C++ templates at all! :-) >Interesting! I would be curious to see you contrast it with the Py++ >project: > >http://www.language-binding.net/pyplusplus/pyplusplus.html > >to get a sense of when I might choose to use one vs. the other. I know Py++. You cannot compare Py++ with PyBindGen. I would say that PyBindGen replaces Boost.Python. Py++ is a layer on top of Boost.Python. Py++ generates Boost.Python module definition sources through automatic scanning of C++ header files. PyBindGen lacks the header files scanning feature that Py++ provides, and I really miss that feature in PyBindGen. I hope that someone (maybe me) finds time to work on that for PyBindGen, some day... I'm not sure if Py++ is modular enough to be able to receive a different code generation backend besides Boost.Python (Roman, feel free to comment :). Although I like Py++ a lot, I really hate Boost.Python. Maybe it's because of my lack of skill in understanding C++ templates, but I feel like Boost.Python hides too many details underneath a layer of cryptic to follow set of C++ templates, while I need to see the generated code in order to check that memory management details are being declared and implemented correctly. In addition, to compile Boost.Python based bindings your users need to have the boost python library and header files installed. In contrast, PyBindGen generated extensions only require python development header files in order to compile, nothing more. I also think Boost.Pythonextensions compile to rather large modules... Regards, -- Gustavo J. A. M. Carneiro INESC Porto, Telecommunications and Multimedia Unit "The universe is always one step beyond logic." -- Frank Herbert

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Problem with Pyste and simple struct
by Thomas Hauk Sept. 30, 2007

Sept. 30, 2007

Given Foo.h: struct Foo { unsigned char data[4]; }; Pyste produces the following binding: // Module ====================================================================== BOOST_PYTHON_MODULE(PysteTest) { class_< Foo >("Foo", init< >()) .def(init< const Foo& >()) .def_readwrite("data", &Foo::data) ; } When compiled using bjam, produces the following error: ..\..\boost\1_34_1\boost\python\data_members.hpp(64) : error C2440: '=' : cannot convert from 'const unsigned char [4]' to 'unsigned char [4]' There is no context in which this conversion is possible I've poured through the documentation, tutorials, everything, and I haven't found a single example like this. What is wrong, and how do I fix it? T -- Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. --Jamie Zawinski, in comp.lang.emacs

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