Mailman 3 October 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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Re: [C++-sig] new to python; old to C++
by Alan Baljeu Oct. 31, 2008

Oct. 31, 2008

Wow, quiet group. I guess I'll try pybindgen first. Alan Baljeu ----- Original Message ---- From: Alan Baljeu <alanbaljeu(a)yahoo.com> To: cplusplus-sig(a)python.org Sent: Friday, October 31, 2008 12:54:39 AM Subject: [C++-sig] new to python; old to C++ Hi all. Question: which python-calling-C++ tool should I try? Background: I need to use Visual Studio 2005 native C++. I know some tools use gcc. That's fine provided it's for something besides compiling my application. I'm looking at Python as a way to accelerate development of a C++ application. This application uses classes enough, but is largely not object oriented. My thought is I would identify a bunch of C++ functions to wrap, wrap them, and then use Python to pull together new functionality. The key to success is to make the C++ aspect of this wrapping as easy as possible. I don't mean "less work" as much as I mean "obvious work that I'm liable to do right because it's simple". If this means restrictions on what interfaces I can expose, I can live with that. Simple means reducing the toolset I need to understand, keeping the input simple, and keeping the output simple. Above all, "Not crashing" is a priority for me. Alan Baljeu __________________________________________________________________ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now at http://ca.toolbar.yahoo.com. _______________________________________________ Cplusplus-sig mailing list Cplusplus-sig(a)python.org http://mail.python.org/mailman/listinfo/cplusplus-sig __________________________________________________________________ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now at http://ca.toolbar.yahoo.com.

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new to python; old to C++
by Alan Baljeu Oct. 31, 2008

Oct. 31, 2008

Hi all. Question: which python-calling-C++ tool should I try? Background: I need to use Visual Studio 2005 native C++. I know some tools use gcc. That's fine provided it's for something besides compiling my application. I'm looking at Python as a way to accelerate development of a C++ application. This application uses classes enough, but is largely not object oriented. My thought is I would identify a bunch of C++ functions to wrap, wrap them, and then use Python to pull together new functionality. The key to success is to make the C++ aspect of this wrapping as easy as possible. I don't mean "less work" as much as I mean "obvious work that I'm liable to do right because it's simple". If this means restrictions on what interfaces I can expose, I can live with that. Simple means reducing the toolset I need to understand, keeping the input simple, and keeping the output simple. Above all, "Not crashing" is a priority for me. Alan Baljeu __________________________________________________________________ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now at http://ca.toolbar.yahoo.com.

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boost::python constructing object from PyObject *
by Dan Eloff Oct. 30, 2008

Oct. 30, 2008

When creating an object from a PyObject *, how do you distinguish between a PyObject pointer that is a new reference (must not be increfed, but must be decrefed) versus a PyObject * that is a borrowed reference? (should be increfed and decrefed) A very simple question for which there is no documented answer, conflicting answers in the archives of this mailing list, and hours of googling has turned up conflicting information. The best I could find was object(borrowed(ptr)) for new references and object(handle<>(ptr)) for borrowed pointers. I'm not sure if that is accurate, but if so that deserves a nomination for a terrible interface award. Please someone put me out of my misery. What's the interface for this? -Dan

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Calling import() multiple times for the same module
by Robert Dailey Oct. 27, 2008

Oct. 27, 2008

Hi, What happens if I do the following? using namespace boost::python; import( "__main__" ).attr( "new_global" ) = 40.0f; import( "__main__" ).attr( "another_global" ) = 100.0f: My main concern here is performance. I'm wondering if each call to import() results in a disk query for the script in question and loads it from there. I'm also wondering if the second import() above will simply read from a memory cache or something. Help would be appreciated.

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[c++-sig] python std::string assignment
by Furkan Kuru Oct. 26, 2008

Oct. 26, 2008

Hello, I have exported a struct containing a std::string field and used it one of my py files. I used same py and pyd file in another operating system (vista). It just stuck without giving any errors. I figured out that the std::string field gets a limited space (as it should do) but does not increase it when initialized or assigned with longer sequence of characters. Is it a "quick and good" solution to write a wrapper for std::string and set its reserved space a high number ( reserve(128); ) or export overloaded = operator to python side? thanks in advance. -- Furkan Kuru

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