Mailman 3 December 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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Enums with duplicated values.
by Hugo Lima Feb. 10, 2009

Feb. 10, 2009

Hi; I need wrap enums with duplicated values, but boost::python do not support it. At the boost website you can find the quote: "Scott Snyder provided a patch; Dave was dissatisfied for some reason, but maybe it should just be applied if no further action occurs http://aspn.activestate.com/ASPN/Mail/Message/1824616." Why this patch was not been accepted since 2003? What can we do to get this patch accepted, so we do not have to maintain a boost-copy on our repositories?

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Re: [C++-sig] Pickle an enum from c++
by Matthew Scouten (TT) Jan. 26, 2009

Jan. 26, 2009

>From the lack of response I assume that no one has any clever ideas to make an enum pickleable. Thank you to anyone who put thought into this. If I come up anything that works, I will let the group know. From: Matthew Scouten (TT) Sent: Tuesday, December 02, 2008 2:24 PM To: Development of Python/C++ integration Subject: Pickle an enum from c++ I have an enum in my c++ library. In fact I have a crap load of them. 169 to be exact. I need them to be pickle-able. The enum_ object does not have a .def_pickle function, so I cannot use the pickle suite. I tried to just up and pickle it but that does not work either. enum box {cardboard, cereal, toy}; BOOST_PYTHON_MODULE(busybox) { enum_<box>("box") .value("cardboard",cardboard ) .value("cereal",cereal ) .value("toy", toy); } C:\Documents and Settings\mscouten>cd C:\tt-dev\manticore\ C:\tt-dev\manticore>call setpath.bat Python 2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1310 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> import pickle, busybox >>> >>> b = busybox.box.toy >>> >>> bs = pickle.dumps(b) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python25\lib\pickle.py", line 1366, in dumps Pickler(file, protocol).dump(obj) File "C:\Python25\lib\pickle.py", line 224, in dump self.save(obj) File "C:\Python25\lib\pickle.py", line 331, in save self.save_reduce(obj=obj, *rv) File "C:\Python25\lib\pickle.py", line 401, in save_reduce save(args) File "C:\Python25\lib\pickle.py", line 286, in save f(self, obj) # Call unbound method with explicit self File "C:\Python25\lib\pickle.py", line 562, in save_tuple save(element) File "C:\Python25\lib\pickle.py", line 286, in save f(self, obj) # Call unbound method with explicit self File "C:\Python25\lib\pickle.py", line 748, in save_global (obj, module, name)) pickle.PicklingError: Can't pickle <class '__main__.busybox.box'>: it's not found as __main__.busybox.box >>>

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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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Re: [C++-sig] custom constructor with embedded back reference
by Tim Prepscius Dec. 22, 2008

Dec. 22, 2008

I just wanted to add one more clarification, because actually there is a bug in the code I posted.. For this late binding to work properly.. You really want to have something like this (sorry, ripping from non-test code): template<typename T> struct PAccessorConverter { static PyObject* convert(const T &x) { if (x==0) // i believe this is sending back None, not sure have to verify return boost::python::incref(boost::python::object().ptr()); return boost::python::incref(x->getPtr().ptr()); } }; and have that instantiated something like #define IMPLEMENT_PYTHON_CONVERTER(x) \ boost::python::to_python_converter<x *, PAccessorConverter<x *> >(); IMPLEMENT_PYTHON_CONVERTER(myclass) and then when you're doing a class.def, don't return the "existing_reference" because that will somehow cause boost python not to look up the converter.. instead do a return by value... something like: .def("getParentUser", &PCamera::getParentUser, return_value_policy<return_by_value>()) this return_value_policy<return_by_value> queues boost python to search the converters.. which will eventually hit the converter that uses the embedded python object.. (which allows you to have a 1-to-1 relationship between python and c++) -tim

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custom constructor with embedded back reference
by Tim Prepscius Dec. 20, 2008

Dec. 20, 2008

I just wanted to thank http://mail.python.org/pipermail/cplusplus-sig/2007-July/012293.html I've extended what he wrote.. I needed late binding for c++ to python objects. Hope this is useful for someone else. Maybe there was some other way I was supposed to do this, but I couldn't find it. Um.. And yes this code was just cobbled together.. BasePtr is a horrible name I know. :-) #define BOOST_PYTHON_STATIC_LIB #include <boost/python.hpp> #include <boost/detail/lightweight_test.hpp> #include <boost/python/module.hpp> #include <iostream> #include <map> namespace python = boost::python; class Base; //------------------------------------------------------ #define IMPLEMENT_PYTHON_ACCESSOR_H \ public: \ static void setClass (boost::python::object _clazz) { clazz = _clazz; } \ static boost::python::object getClass() { return clazz; } \ virtual void reflectBind (boost::python::object object) \ { \ ::bind(this, object); \ } \ private: \ static boost::python::object clazz; \ #define IMPLEMENT_PYTHON_ACCESSOR_CPP(x) \ boost::python::object x::clazz; //------------------------------------------------------ template<typename T> void bind (T *self, boost::python::object object) { // Insert new S object pointer into python object typedef boost::python::objects::pointer_holder<T *, T> holder; typedef boost::python::objects::instance<holder> instance_t; void* memory = holder::allocate( object.ptr(), offsetof(instance_t, storage), sizeof(holder) ); try { (new (memory) holder(self))->install(object.ptr()); } catch(...) { holder::deallocate(object.ptr(), memory); throw; } } //------------------------------------------------------ class BasePtr { public: BasePtr() { std::cout << this; }; virtual ~BasePtr () { }; virtual void reflectBind (boost::python::object pyobject) { } void bind (boost::python::object pyobject) { reflectBind (pyobject); this->object = pyobject; } python::object object; python::object getObject () const { return object; } void doBind (python::object o) { bind( o); } static python::object nowhere (python::object); } ; //---------------------------------------------------- class Base : public BasePtr { IMPLEMENT_PYTHON_ACCESSOR_H public: virtual ~Base() { }; Base () { } virtual std::string hello() { std::cout << this; return "Base says hello"; } virtual Base *myself () { return this; } }; IMPLEMENT_PYTHON_ACCESSOR_CPP (Base); class Inherited : public Base { IMPLEMENT_PYTHON_ACCESSOR_H public: Inherited () { } virtual ~Inherited () { } std::string hello() { std::cout << this; return "Inherited says hello"; } } ; IMPLEMENT_PYTHON_ACCESSOR_CPP (Inherited); /* Not needed after all template<typename T> struct BaseToReference { static PyObject* convert(const T &x) { if (&x == 0) return python::incref(python::object().ptr()); return python::incref(x.getObject().ptr()); } }; */ python::object BasePtr::nowhere (python::object pyobject) { return python::object(); } //--------------------------------------------------- BOOST_PYTHON_MODULE(embedded_hello) { Base::setClass( python::class_<Base, boost::noncopyable> ("Base", python::no_init) .def("__init__", &BasePtr::nowhere) .def ("hello", &Base::hello, python::return_value_policy<python::return_by_value>()) .def ("myself", &Base::myself, python::return_value_policy<python::reference_existing_object>()) ); Inherited::setClass ( python::class_<Inherited, python::bases<Base>, boost::noncopyable> ("Inherited", python::no_init) .def("__init__", &BasePtr::nowhere) .def ("hello", &Inherited::hello, python::return_value_policy<python::return_by_value>()) ); // not needed after all // python::to_python_converter<Base, BaseToReference<Base> >(); } //--------------------------------------------------- int main(int argc, char **argv) { // Initialize the interpreter Py_Initialize(); bool error_expected = false; if (PyImport_AppendInittab("embedded_hello", initembedded_hello) == -1) throw std::runtime_error("Failed to add embedded_hello to the interpreter's " "builtin modules"); PyObject *z2 = PyImport_ImportModule ("embedded_hello"); python::object module (python::handle<>(PyImport_ImportModule ("embedded_hello"))); python::object dict = module.attr("__dict__"); // Retrieve the main module python::object main = python::import("__main__"); // Retrieve the main module's namespace python::object global(main.attr("__dict__")); python::object result1 = python::exec( "from embedded_hello import * \n" "class PythonDerived(Base): \n" " def __init__(self): \n" " Base.__init__(self); \n" "\n" " def hello(self): \n" " print 'hello from python' \n" " print Base.hello(self) \n" " return 'Hello from Python!' \n" "\n" " def test(self): \n" " print 'test1 says ' \n" " print self.myself().hello()\n" , global, global); Base b; b.doBind(global["PythonDerived"]()); python::object o(b.object); ; python::object r = o.attr("hello")(); o.attr("test")(); python::object result2 = python::exec( "from embedded_hello import * \n" "class PythonDerived2(Inherited): \n" " def __init__(self): \n" " Inherited.__init__(self); \n" "\n" " def hello(self): \n" " print 'hello from python' \n" " print Inherited.hello(self) \n" " return 'Hello from Python!' \n" "\n" " def test(self): \n" " print 'test2 says ' \n" " print self.myself().hello()\n" , global, global); Inherited c; c.doBind(global["PythonDerived2"]()); python::object oc(c.object); ; python::object rc = oc.attr("hello")(); oc.attr("test")(); std::cout << "success!" << std::endl; }

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pyste and compressed_pair
by Dmitriy Morozov Dec. 20, 2008

Dec. 20, 2008

Hi, If I have the simplest header file that includes compressed_pair.hpp, and I run pyste on it, pyste crashes complaining about is_abstract.hpp included from compressed_pair.hpp. An example and error messages are below. I was wondering if this was a known problem, and if there are any workarounds. I'm trying this right now with Boost 1.36.0, but I believe the same problem occurs with 1.37.0 (I tried it earlier). Thanks in advance for your help. Dmitriy test.h: #include <boost/compressed_pair.hpp> struct A { int a; }; test.pyste: Class("A", "test.h") When running "pyste.py test.pyste" I get: In file included from /usr/include/boost/type_traits/is_convertible.hpp:25, from /usr/include/boost/type_traits/is_empty.hpp:12, from /usr/include/boost/detail/compressed_pair.hpp:26, from /usr/include/boost/compressed_pair.hpp:21, from test.h:1: /usr/include/boost/type_traits/is_abstract.hpp:72: error: expected primary-expression before ')' token /usr/include/boost/type_traits/is_abstract.hpp:72: error: a function call cannot appear in a constant-expression In file included from /usr/include/boost/type_traits/is_empty.hpp:19, from /usr/include/boost/detail/compressed_pair.hpp:26, from /usr/include/boost/compressed_pair.hpp:21, from test.h:1: /usr/include/boost/type_traits/is_class.hpp:122: error: expected primary-expression before ')' token /usr/include/boost/type_traits/is_class.hpp:122: error: a function call cannot appear in a constant-expression Traceback (most recent call last): File "/usr/bin/pyste.py", line 8, in <module> pyste.main() File "/usr/lib/python2.5/site-packages/Pyste/pyste.py", line 418, in main status = Begin() File "/usr/lib/python2.5/site-packages/Pyste/pyste.py", line 257, in Begin return GenerateCode(parser, module, out, interfaces, multiple) File "/usr/lib/python2.5/site-packages/Pyste/pyste.py", line 376, in GenerateCode declarations, parsed_header = parser.Parse(header, interface, tail) File "/usr/lib/python2.5/site-packages/Pyste/CppParser.py", line 165, in Parse declarations = self.ParseWithGCCXML(header, tail) File "/usr/lib/python2.5/site-packages/Pyste/CppParser.py", line 126, in ParseWithGCCXML raise CppParserError, 'Error executing gccxml' Pyste.CppParser.CppParserError: Error executing gccxml

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