Mailman 3 July 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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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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static/dynamic boost::python conflicts?
by Koichi Tamura Aug. 7, 2008

Aug. 7, 2008

Hello, I'm using boost::python and I've got a problem now. I'm writing a shared library(bundle, I'm using MacOSX10.5, and it's a plug-in for some application) where I have a code like this. //....on init.... if ( ! Py_IsInitialized()) { int a = PyImport_AppendInittab("MyModule", &initMyModule); Py_Initialize(); PyEval_InitThreads(); PyEval_ReleaseLock(); } //....somewhere else... PyGILState_STATE state = PyGILState_Ensure(); module = object(handle<>(PyModule_New(moduleName))); myMod = object(handle<>(PyImport_ImportModule("MyModule"))); module.attr("mymod") = myMod; PyGILState_Release(state); I statically linked boost::python, and it works fine. When imported, MyModule is filled with classes that boost::python has wrapped. But when I use another shared library(#) which dynamically links boost::python together with mine, PyImport_ImportModule("MyModule") returns a module which dict is empty but __doc__ and __name__. Instead of (#) I made a test shared library that does nothing but linking boost::python dynamically, and it still fails. Why does all statically linked boost::python and extension is affected by a dynamically linked boost::python? I'm really puzzled. I would really appreciate if anybody could help. -Koichi

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application exit and shared_ptr
by Philip Winston Aug. 7, 2008

Aug. 7, 2008

I understand it is not possible to call Py_Finalize with Boost.Python. But is it possible to manually delete all variables from an embedded interactive interpreter? Would this be a way to to cause Python to release any shared_ptrs it is holding on to? So we return shared_ptrs from our API. But at exit (and possibly other times) we'd like to reset the interpreter, so it's no longer holding any shared_ptrs, so those objects are free to be deleted if no other references are held. Some specific excerpts (any other advice welcome): excerpts: m_mainmodule = import("__main__"); m_namespace = m_mainmodule.attr("__dict__"); exec("import PyInteractive"); exec("__pyInteractiveExec = PyInteractive.PyInteractive().executeline"); m_interactive = extract<object>(m_namespace["__pyInteractiveExec"]); then we repeatedly call: m_interactive(string); S now we'd like to delete all objects the user created interactively at the prompt. Thanks. Philip Winston pwinston(a)gmail.com

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Crash (segfault) on del(x.__dict__) where x is a boost.python wrapped instance.
by Alex Mohr July 31, 2008

July 31, 2008

Tested with boost 1.34 on x86-64 linux, gcc 4.1.2. I have attached a very small example below. I know that del(x.__dict__) is a rather odd thing to try to do, and we stumbled upon this by accident. It is not a big deal for us. That said, it might be nice to fix if it's easy. Thanks, Alex //////////////////////////////////////////////////////////////////////// // C++ #include <boost/python/class.hpp> class X {}; BOOST_PYTHON_MODULE(del_dict_segfault) { boost::python::class_<X>("X"); } ######################################################################## ## Python >>> from del_dict_segfault import X >>> x = X() >>> del(x.__dict__) # this segfaults.

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external constructors
by Gennadiy Rozental July 29, 2008

July 29, 2008

Hi, is there any way to register external constructor for C++ class? Specifically If I have class class A { ... }; I want to register constructor like this: class_<A>(...) .def( "__init__", &make_A ) where make_A is defined something like: void make_A( A&, boost::python::list const& ); Doesn't seem to work like this. Gennadiy

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