Mailman 3 November 2008 - 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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Bug and patch for boost.python with enable_shared_from_this
by Chad Austin March 26, 2009

March 26, 2009

Hi all, A month ago or so we discovered a bug in Boost.Python that manifests when using enable_shared_from_this. Here is a test case that demonstrates the bug: #include <boost/python.hpp> #include <boost/enable_shared_from_this.hpp> using namespace boost; using namespace boost::python; class Test; typedef shared_ptr<Test> TestPtr; class Test : public enable_shared_from_this<Test> { public: static TestPtr construct() { return TestPtr(new Test); } void act() { TestPtr kungFuDeathGrip(shared_from_this()); } void take(TestPtr t) { } }; void Export_test() { class_<Test, TestPtr, noncopyable>("Test") .def("construct", &Test::construct) .staticmethod("construct") .def("act", &Test::act) .def("take", &Test::take) ; } And here is the Python: x = Test.construct() x.take(x) x.act() The bug (as I understand it) is that the shared_ptr_from_python converter creates a new shared_ptr for the Test instance to pass it into C++. This new shared_ptr has a nop deleter, except that it keeps the Python object alive as long as the new shared_ptr is alive. The problem here is that creating a shared_ptr to an object of type T when T is enable_shared_from_this<T> resets the weak pointer inside of enable_shared_from_this<T>. (See shared_ptr's constructors for the details of the implementation.) A fix that passes the test above and has worked for us is to change shared_ptr's constructor to accept a dont_enable_shared_from_this argument and pass that in from the shared_ptr_from_python converter. The patch is attached (against boost 1.33, but the bug didn't look fixed in 1.34 either). Cheers, Chad p.s. I have seen other people with this problem as well. Googling for bad_weak_ptr turns up several results.

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py++ with template member function of template class
by Soloman Jan. 16, 2009

Jan. 16, 2009

Hi, I have met a problem using py++ (pyplusplus) to generate code. First, let's see this code: //////////////////////////////////////////////////////////////////////////////////// // template member function class AFunc { public: template <typename T> T foo(const T& t) const { return t + 1; } }; // we can only fully specialize function template <> string AFunc::foo<string>(const string& t) const { return "string"; }; // the following code is used to generate the instance of template functions #ifdef PYTHONWRAP void AFuncInit() { AFunc a; cout << a.foo<int>(1) << endl; cout << a.foo<float>(1.5f) << endl; cout << a.foo<string>("hello") << endl; }; #endif I followed the instruction in py++ homepage->FAQ, and this works, a call to a.foo<int> will generate an instance of that template member function. But, then, I used template class, and it won't work any more: ///////////////////////////////////////////////////////////////////////// // test template member function in template class // THIS WON'T WORK!!!!!!!!!!!!! template <typename A> class BFunc { public: template <typename T> T foo(const T& t) const; }; template <typename A> template <typename T> T BFunc<A>::foo(const T& t) const { return t + 1; }; #ifdef PYTHONWRAP typedef BFunc<int> BFunc_Int; void BFuncInit() { BFunc_Int a; //mem_fun(&BFunc_Int::foo<int>); //void * p = (void *)(&BFunc<int>::template foo<int>); cout << a.foo<int>(2) << endl; cout << a.foo<float>(2.5) << endl; //cout << a.foo<string>("hello") << endl; }; #endif Look into the generated code, I saw: bp::class_< AFunc >( "AFunc" ) .def( "foo" , (::std::string ( ::AFunc::* )( ::std::string const & ) const)( &::AFunc::foo ) , ( bp::arg("t") ) ) .def( "foo" , (float ( ::AFunc::* )( float const & ) const)( &::AFunc::foo ) , ( bp::arg("t") ) ) .def( "foo" , (int ( ::AFunc::* )( int const & ) const)( &::AFunc::foo ) , ( bp::arg("t") ) ); bp::class_< BFunc< int > >( "BFunc_Int" ); obviously, a call to BFunc_Int::foo<int> hasn't create the template member function instance, can anybody help me? Regards, Xiang.

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Re: [C++-sig] Bug and patch for boost.python with enable_shared_from_this
by Ralf W. Grosse-Kunstleve Dec. 23, 2008

Dec. 23, 2008

No news that I'm aware of. I'd be happy to check in patches, but someone else has to take the lead in communicating with Peter, and updating the unit tests. Ralf ----- Original Message ---- From: Edson Tadeu <e.tadeu(a)gmail.com> To: Development of Python/C++ integration <c++-sig(a)python.org> Sent: Thursday, February 28, 2008 11:45:32 AM Subject: Re: [C++-sig] Bug and patch for boost.python with enable_shared_from_this Any news on this issue? Will this patch get into Boost 1.35? Thanks, Edson On Wed, Feb 13, 2008 at 5:27 PM, Ralf W. Grosse-Kunstleve <rwgk(a)yahoo.com> wrote: Hi Chad, Could you at least ask Peter Dimov if he thinks the dont_enable_shared_from_this patch could be generally useful? Maybe he's OK adding it, then it wouldn't be a big deal fixing Boost.Python, which would probably prevent a lot of confusion and lost time in the future. http://www.boost.org/people/peter_dimov.htm p-d-i-m-o-v-at-m-m-l-t-d-dot-n-e-t Ralf ----- Original Message ---- From: Chad Austin <chad(a)imvu.com> To: Development of Python/C++ integration <c++-sig(a)python.org> Sent: Monday, February 11, 2008 10:10:31 PM Subject: Re: [C++-sig] Bug and patch for boost.python with enable_shared_from_this There probably is a way to prevent boost.python from creating shared_ptrs with a null deleter like it does, but it would require far more knowledge than I have. :) I agree that it would be a better fix, though. On 2/11/08, Ralf W. Grosse-Kunstleve <rwgk(a)yahoo.com> wrote: > > > > Thanks for the patch! I'd love to check this in for you, but for the > change in shared_ptr.hpp you'll need Peter Dimov's approval, and the > shared_ptr documentation would have to be updated. Also, your reproducer > should be turned into a unit test (in boost/libs/python/test). > > Is there any chance that the shared_ptr patch could somehow be avoided? > > Ralf > > > > ----- Original Message ---- > From: Chad Austin <chad(a)imvu.com> > To: c++-sig(a)python.org > Sent: Sunday, February 10, 2008 5:14:45 PM > Subject: [C++-sig] Bug and patch for boost.python with enable_shared_from_this > > Hi all, > > A month ago or so we discovered a bug in Boost.Python that manifests when using enable_shared_from_this. Here is a test case that demonstrates the bug: > > ... -----Inline Attachment Follows----- _______________________________________________ C++-sig mailing list C++-sig(a)python.org http://mail.python.org/mailman/listinfo/c++-sig

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Passing C++ instance to embedded py
by fileoffset Dec. 14, 2008

Dec. 14, 2008

To best explain my problem, here is some code: struct A { A() { mTest = 1; std::cout << "Test: " << mTest; Py_Initialize(); object main_module = import("__main__"); object main_namespace = main_module.attr("__dict__"); main_namespace["A_Instance"] = this; object result = exec_file(str("test.py"), main_namespace, main_namespace); std::cout << "Test: " << mTest; } int mTest; } in main.cpp or similar: BOOST_PYTHON_MODULE(MyModule) { class_<A>("A", init<>()) .def_readwrite("Test", &A::mTest) ; } test.py: from MyModule import * A_Instance.Test = 5 Essentially I want to be able to access and modify the properties of an instance of a C++ class at runtime. When I try code similar to above, python excepts, as I believe it attempts to copy-construct the A class instead of just pass the reference (this) so that i can modify it. Is what I want possible? If not what would be a better way to do it? -- file offset <fileoffset(a)gmail.com>

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wrapper and shared_ptr - how to combine?
by Leonard Ritter Dec. 3, 2008

Dec. 3, 2008

i am wrapping an abstract class "Actor" which is to be implemented partially in Python, using a wrapper class that looks like this: class PyActor : public Actor, public wrapper<Actor> { public: .... }; the boost.python export code looks like this: class_<PyActor, boost::noncopyable>("Actor"); this would be all good and well, until I decided to pass back Actor pointers from methods e.g. like Actor::get_parent(), which have to resolve back to original python objects, for which the FAQ suggests using shared_ptr, if altering the underlying code was possible - which it is. so there is now a method in Actor declared like this: // assumed: typedef boost::shared_ptr<Actor> ActorPtr; ActorPtr Actor::get_parent(); unfortunately calling that method gives me a new wrapped Actor python object - not exactly what the FAQ promised. but I read that the shared_ptr<> has to be declared as the object holder, like this: class_<PyActor, ActorPtr, boost::noncopyable("Actor"); which I did, but that gives me a compiler error if Actor is abstract, and if I declare it non-abstract, calls to wrapping PyActor methods fail in Python. I guess that this approach does not work with wrapper classes, or the syntax is different. how do I have to do it? I searched through the mailing list but found nothing viable so far. thanks in advance!

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shared_ptr with custom destructor
by Renato Araujo Dec. 1, 2008

Dec. 1, 2008

Hi all, I would like to specify during the class_ declaration use a shared_ptr with custom release function. shared_ptr has a constructor where you can pass a function to call in the release, I would like to use this in a generic form. I already tried some like that: shared_ptr<BaseClass> _custom_constructor() { return shared_ptr<BaseClass>(new BaseClass(), _release_func); } class_ <BaseClass, shared_ptr<BaseClass> > ("BaseClass").def("__init__", make_constructor(_custom_constructor)); but this not work to class derived from BaseClass: my _custom_constructor is not called to others class. I would like something more generic where I can declare in class_ template, something like that: class_<MyClass, boost::shared_ptr<MyClass, release_func> ("MyObject") ....... There is something like that? How is the best way to do this? BR -- Renato Araujo Oliveira Filho

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Pyste,Py++: equivalent of swig typemaps?
by Mihail Konstantinov Nov. 30, 2008

Nov. 30, 2008

Hello, due to limitations of swig I am currently learning Py++ and Pyste (because it seems currently to be better documented than Py++). Does Pyste or Py++ offer typemaps like swig (http://www.swig.org/Doc1.3/SWIGDocumentation.html#Python_nn53) that allow any sequence of input arguments to be wrapped to other Python arguments (like for example ...,int len,char *s,... to a Python string) in any function where they appear, even surrounded by other arguments? The only remotely similar I found documented is http://www.boost.org/doc/libs/1_37_0/libs/python/pyste/doc/wrappers.html which explains how to write a wrapper between C++ STL and Python containers. But such a wrapper has to be rewritten for each and every function. Is there a simple method that automates the repetitive task like swig typemaps? Thanks Mihail

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Re: [C++-sig] [pygccxml-development] Pyste, Py++: equivalent of swig typemaps?
by Roman Yakovenko Nov. 30, 2008

Nov. 30, 2008

On Sun, Nov 30, 2008 at 8:58 PM, Mihail Konstantinov <kmihail(a)rocketmail.com> wrote: > Hello, > due to limitations of swig I am currently learning Py++ and Pyste (because > it seems currently to be better documented than Py++). Hmm. Did you see http://language-binding.net/pyplusplus/pyplusplus.html page? If so what documentation you think it lacks or what could be improved? > Does Pyste or Py++ offer typemaps like swig > (http://www.swig..org/Doc1.3/SWIGDocumentation.html#Python_nn53) that allow > any sequence of input arguments to be wrapped to other Python arguments > (like for example ....,int len,char *s,... to a Python string) in any > function where they appear, even surrounded by other arguments? > > The only remotely similar I found documented is > http://www.boost.org/doc/libs/1_37_0/libs/python/pyste/doc/wrappers.html > which explains how to write a wrapper between C++ STL and Python containers. > But such a wrapper has to be rewritten for each and every function. Is there > a simple method that automates the repetitive task like swig typemaps? I can answer for Py++ only. If I understand right, SWIG typemaps, than you are looking for "Function Transformation" feature: http://language-binding.net/pyplusplus/documentation/functions/transformati… If you combine it with "query" functionality ( http://language-binding.net/pygccxml/query_interface.html ) you get what you want. HTH -- Roman Yakovenko C++ Python language binding http://www.language-binding.net/

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