Mailman 3 February 2015 - Cplusplus-sig

Re: [C++-sig] Cplusplus-sig Digest, Vol 76, Issue 6
by Botos, Christopher Feb. 23, 2015

Feb. 23, 2015

Well, I'm embarrassed. I don't believe I did that. Thanks so much! ________________________________________ From: Cplusplus-sig [cplusplus-sig-bounces+cbotos=aer.com(a)python.org] on behalf of cplusplus-sig-request(a)python.org [cplusplus-sig-request(a)python.org] Sent: Monday, February 23, 2015 6:00 AM To: cplusplus-sig(a)python.org Subject: Cplusplus-sig Digest, Vol 76, Issue 6 Send Cplusplus-sig mailing list submissions to cplusplus-sig(a)python.org To subscribe or unsubscribe via the World Wide Web, visit https://mail.python.org/mailman/listinfo/cplusplus-sig or, via email, send a message with subject or body 'help' to cplusplus-sig-request(a)python.org You can reach the person managing the list at cplusplus-sig-owner(a)python.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Cplusplus-sig digest..." Today's Topics: 1. Re: Wrapping virtual method returning void (Holger Joukl) ---------------------------------------------------------------------- Message: 1 Date: Mon, 23 Feb 2015 08:52:49 +0100 From: Holger Joukl <Holger.Joukl(a)LBBW.de> To: Development of Python/C++ integration <cplusplus-sig(a)python.org> Subject: Re: [C++-sig] Wrapping virtual method returning void Message-ID: <OF2DB1123C.ACFE992C-ONC1257DF5.002A8ACD-C1257DF5.002B49AA(a)LBBW.de> Content-Type: text/plain; charset=US-ASCII Hi, not boost.python- but C/C++ syntax-related. You never reach the Base class call in your wrapper class: > struct SongWrapper : Song, bp::wrapper<Song> > { > void chorus() > { > if (bp::override chorus = this->get_override("chorus")) > chorus(); > return; <------------ Called unconditionally > Song::chorus(); > return; > } > > void default_chorus() { this->Song::chorus(); } > }; I suggest using proper {} brackets and indentation with if-else constructs for readability. Your int-returning member function doesn't suffer from this problem: > > struct AnotherSongWrapper : AnotherSong, bp::wrapper<AnotherSong> > { > int chorus() > { > if (bp::override chorus = this->get_override("chorus")) > return chorus(); > return AnotherSong::chorus(); > } > > int default_chorus() { return this->AnotherSong::chorus(); } > }; Holger Landesbank Baden-Wuerttemberg Anstalt des oeffentlichen Rechts Hauptsitze: Stuttgart, Karlsruhe, Mannheim, Mainz HRA 12704 Amtsgericht Stuttgart ------------------------------ Subject: Digest Footer _______________________________________________ Cplusplus-sig mailing list Cplusplus-sig(a)python.org https://mail.python.org/mailman/listinfo/cplusplus-sig ------------------------------ End of Cplusplus-sig Digest, Vol 76, Issue 6 ******************************************** ________________________________ This email is intended solely for the recipient. It may contain privileged, proprietary or confidential information or material. If you are not the intended recipient, please delete this email and any attachments and notify the sender of the error.

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Wrapping virtual method returning void
by Botos, Christopher Feb. 23, 2015

Feb. 23, 2015

I have an example C++ base class (Song) with a virtual method (chorus) returning void that is called by another method (play) of the same class. I want to be able to derive a python class from this and override the virtual method. I experience the following behavior: 1. If I simply instantiate the wrapped base class in python and call play, **the virtual chorus is never entered/executed**. 2. If I create a derived class and override the virtual chorus, the derived chorus is executed correctly. 3. If I change the base class chorus to return int (or anything) instead of void, the base class chorus is executed correctly. I have wrapped my class as described here: http://www.boost.org/doc/libs/1_43_0/libs/python/doc/v2/wrapper.html My example C++, python code, and output python output is below (I've tried to make it as concise as possible). I can work around this issue in my application by having my virtual method return an unused object, although this is not ideal. I would appreciate any other suggestions, whether I'm doing something incorrectly, or is this possibly a boost python bug? //------------------------------------------------ // Has virtual method returning void // Numbers indicate order in which the print statements should appear. //------------------------------------------------ class Song { public: virtual ~Song(){} void play() { std::cout << "\n1) Base class --> Song.play" << std::endl; chorus(); std::cout << "3) Base class <-- Song.play" << std::endl; } // THIS METHOD IS NEVER EXECUTED virtual void chorus() { std::cout << "2) Base class Song.chorus returning void" << std::endl; } }; struct SongWrapper : Song, bp::wrapper<Song> { void chorus() { if (bp::override chorus = this->get_override("chorus")) chorus(); return; Song::chorus(); return; } void default_chorus() { this->Song::chorus(); } }; //------------------------------------------------ // Has virtual method returning int // Numbers indicate order in which the print statements should appear. //------------------------------------------------ class AnotherSong { public: virtual ~AnotherSong(){} void play() { std::cout << "\n1) Base class --> AnotherSong.play" << std::endl; chorus(); std::cout << "3) Base class <--AnotherSong.play" << std::endl; } // THIS METHOD (returning int) IS EXECUTED virtual int chorus() { std::cout << "2) Base class AnotherSong.chorus returning int" << std::endl; return 0; } }; struct AnotherSongWrapper : AnotherSong, bp::wrapper<AnotherSong> { int chorus() { if (bp::override chorus = this->get_override("chorus")) return chorus(); return AnotherSong::chorus(); } int default_chorus() { return this->AnotherSong::chorus(); } }; BOOST_PYTHON_MODULE(Songs) { bp::class_<SongWrapper,boost::noncopyable>("Song") .def("play", &Song::play) .def("chorus", &Song::chorus, &SongWrapper::default_chorus) ; bp::class_<AnotherSongWrapper,boost::noncopyable>("AnotherSong") .def("play", &AnotherSong::play) .def("chorus", &AnotherSong::chorus, &AnotherSongWrapper::default_chorus) ; } #------------------------------------------------ # Python file ... #------------------------------------------------ from Songs import Song, AnotherSong # Base class chorus returning void is not executed: step 2 is missing in the output s1 = Song() s1.play() # Derived class chorus is executed: step 2 in the output class Chart(Song): def chorus(self): print "** 2) Derived class Chart.chorus" c1 = Chart() c1.play() # Base class chorus returning int is executed: step 2 in output s2 = AnotherSong() s2.play() #------------------------------------------------ # Python output ... # In first case, step 2 is missing ... chorus was not executed #------------------------------------------------ 1) Base class --> Song.play 3) Base class <-- Song.play 1) Base class --> Song.play ** 2) Derived class Chart.chorus 3) Base class <-- Song.play 1) Base class --> AnotherSong.play 2) Base class AnotherSong.chorus returning int 3) Base class <--AnotherSong.play ________________________________ This email is intended solely for the recipient. It may contain privileged, proprietary or confidential information or material. If you are not the intended recipient, please delete this email and any attachments and notify the sender of the error.

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passing by non-const reference?
by Christopher O'Grady Feb. 19, 2015

Feb. 19, 2015

Hi, Based on websearches we have done, we believe that boost-python does not allow passing arguments by non-const-reference (at least, not easily). Can someone confirm this is still the case, or point me to some documentation that discusses it? We think this prevents us from return multiple arguments from a method call. Looking through the mailing list archives, we believe this is impossible. If someone knows differently can you let us know? Thanks! chris

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Boost.Python: Review of Patches
by Huebl, Axel Feb. 12, 2015

Feb. 12, 2015

Hi, I was directed here from the Boost groups homepage http://www.boost.org/community/groups.html#cplussig so I hope my question is well placed. I was wondering if, how and when patches for Boost.Python (specially bug fixes) are merged. When I reported two bugs (including patches) beginning of the month (that sounds a bit impatient - so if I am just pushing to much just tell me) in both trac and on GitHub: https://svn.boost.org/trac/boost/ticket/10932 https://svn.boost.org/trac/boost/ticket/10933 I noticed that there are other pull requests since at least two boost stable releases on GitHub https://github.com/boostorg/python/pulls (some of them also with a trac issue) that have not yet been reviewed/included/commented-on/closed in the code base even if they are most of the time straight forward fixes. My background: I am combined Boost.Python with via cmake with an open source, (mpi) parallel, many-GPGPU code [1] compiled with nvcc 6.5 and noted some minor compile errors in Boost.Python that can be fixed quite easily. (Btw: it works like a charm, thank you so much!) Best regards, Axel Huebl [1] http://picongpu.hzdr.de -- Axel Huebl Phone +49 351 260 3582 https://www.hzdr.de/crp Computational Radiation Physics Laser Particle Acceleration Division Helmholtz-Zentrum Dresden - Rossendorf e.V. Bautzner Landstrasse 400, 01328 Dresden POB 510119, D-01314 Dresden Vorstand: Prof. Dr.Dr.h.c. R. Sauerbrey Prof. Dr.Dr.h.c. P. Joehnk VR 1693 beim Amtsgericht Dresden

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