Mailman 3 January 2009 - 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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built-in submodule creation
by Tim Prepscius Feb. 8, 2009

Feb. 8, 2009

Greetings, I am trying to create built-in sub modules.. I have read everything I can on this subject.. And I've tried many many possible solutions.. And lost many hours actually (blech). Some of the e-mails in these newsgroups from long ago are quite misleading.. Other e-mails on this topic seem to be inaccessible. Much of "piper-mail" is gone it seems, or relocated beyond the reach of google. (didn't know that was still possible!) The only solution that works so far: given that I've created dD_script and dD_object and dD* modules previously.. object dD = object(handle<>(PyImport_AddModule ("dD"))); char *statement = // import what I need, I guess I don't need types actually "import sys, types\n"\ // this is importing all of the modules that I've already created.. "import dD, dD_script, dD_object, dD_types, dD_ui, dD_device, dD_render, dD_internal\n"\ // this is assigning them to the parent "package" "dD.Script = sys.modules['dD.Script'] = dD_script\n"\ "dD.Object = sys.modules['dD.Object'] = dD_object\n"\ "dD.Types = sys.modules['dD.Types'] = dD_types\n"\ "dD.UI = sys.modules['dD.UI'] = dD_ui\n"\ "dD.Device = sys.modules['dD.Device'] = dD_device\n"\ "dD.Render = sys.modules['dD.Render'] = dD_render\n"\ "dD.Internal = sys.modules['dD.Internal'] = dD_internal"\ ; exec(statement, mainDict, mainDict); The non-solutions that don't work: object dD = object(handle<>(PyImport_AddModule ("dD"))); dD.attr("Script") = handle<>(PyImport_ImportModule("dD_script")); dD.attr("Object") = handle<>(PyImport_ImportModule("dD_object")); dD.attr("Types") = handle<>(PyImport_ImportModule("dD_types")); dD.attr("UI") = handle<>(PyImport_ImportModule("dD_ui")); dD.attr("Device") = handle<>(PyImport_ImportModule("dD_device")); dD.attr("Render") = handle<>(PyImport_ImportModule("dD_render")); dD.attr("Internal") = handle<>(PyImport_ImportModule("dD_internal")); I also tried manipulating the dictionary of the dD module instead of attributes above object sys = import("sys"); dict sysDict (sys.attr("__dict__")); sysDict["dD.Script"] = dD["Script"]; sysDict["dD.Object"] = dD["Object"]; sysDict["dD.Types"] = dD["Types"]; sysDict["dD.UI"] = dD["UI"]; sysDict["dD.Device"] = dD["Device"]; sysDict["dD.Render"] = dD["Render"]; sysDict["dD.Internal"] = dD["Internal"]; well if dD is the object these direct [] indexes fail, if it is a dict, the solution still doesn't work dict sysModules (sys.attr("modules")); sysModules["dD.Script"] = dD.attr("Script"); sysModules["dD.Object"] = dD.attr("Object"); sysModules["dD.Types"] = dD.attr("Types"); sysModules["dD.UI"] = dD.attr("UI"); sysModules["dD.Device"] = dD.attr("Device"); sysModules["dD.Render"] = dD.attr("Render"); sysModules["dD.Internal"] = dD.attr("Internal"); if I do dict stuff instead of attribute, still doesn't work.. =================== Is there a better way for me to do this, than executing the python code segment? Does anyone know what is going on behind the scenes in the python code execution? Thanks, -tim

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Calling python virtual function from C++
by William Marié Feb. 6, 2009

Feb. 6, 2009

Hi, I have a little problem, i can't find a way to call a pure virtual function from C++ on a Python object taking a specific class object as argument : // Base Class for a component class BaseCmp { public: ~BaseCmp() {}; }; // Base class class Base { public: Base() {}; virtual ~Base() {}; virtual void testVirtualPure( BaseCmp* pBaseCmp ) = 0; }; struct BaseWrap : Base, bp::wrapper<Base> { void testVirtualPure( BaseCmp* pBaseCmp ) { this->get_override("testVirtualPure")( pBaseCmp ); } }; // Module TestScript BOOST_PYTHON_MODULE(test) { // BaseCmp Class exposition bp::class_<BaseCmp,boost::noncopyable>("BaseCmp", bp::no_init) ; // Base Class Wrapper exposition bp::class_<BaseWrap, boost::noncopyable>("Base") .def( "testVirtualPure", bp::pure_virtual( &Base::testVirtualPure ) ) ; } I need to call my testVirtualPure function from C++ side : BaseCmp* bc = BaseCmp(); Base* b = Base(); b->testVirtualPure( bc ); But this causes an error : TypeError: No to_python (by-value) converter found for C++ type: class BaseCmp Does someone know how i can do that ? Thanks a lot -- View this message in context: http://www.nabble.com/Calling-python-virtual-function-from-C%2B%2B-tp217115… Sent from the Python - c++-sig mailing list archive at Nabble.com.

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virtual functions and bind size reduction
by Renato Araujo Feb. 2, 2009

Feb. 2, 2009

Hi guys, Now I'm trying to reduce my python module. To cut the size I've reduced the number of times that I have to expose a function. I had some success while working in the same module, but when dealing with more than one things get complicated. To do this I created a "workaround", described below (very ugly I know but with this I save 6MB, 30%). The problem is that between modules this does not work, there is something wrong during dynamic_cast calls. I will show the basic idea of my solution. (you can check the full code attached) The main idea is: I have my base and derived class like this: =========================================== class Base { protected: virtual void virtual_func() {/*...*/}. }; class Derived : public Base { }; I created a proxy class: ============================================== class BaseProxy { public: virtual void virtual_func_proxy() = 0; }; Now the wrapper class which inherits from my proxy class. ========================================================= Class BaseWrapper : public Base, public wrapper<Base>, public BaseProxy { public: void virtual_func() { } void virtual_func_proxy() { Base::virtual_func_proxy(); } }; Class DerivedWrapper : public Derived, public wrapper<Derived>, public BaseProxy { public: void virtual_func_proxy() { Base::virtual_func_proxy(); } }; Then I create a function which accept my Base class. ==================================================== static void base_virtual_func(Base &self) { //here is the problem this dynamic_cast fails when called from another module BaseProxy *proxy = dynamic_cast<BaseProxy*>(&self); assert(proxy); proxy->virtual_func_proxy(); } Now I export my module ======================= //... class_<BaseWrap, boost::noncopyable>("Base") //with this not is necessary export this function again in derived class .def("virtual_func", base_virtual_func); class_<DerivedWrapper, boost::noncopyable>("Derived"); //... This apparently works fine when running in same module but if I create a class derived from Base in another module (another library), this stop working because the dynamic_cast fails. I'm not sure if this will works in all cases, but this is working fine in my tests when in the same module. I'll appreciate if someone give some idea how solve this, or a another way to save some calls of ".def" functions. -- Renato Araujo Oliveira Filho

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Boost Pro Python Version
by Cameron Royal Jan. 29, 2009

Jan. 29, 2009

So I'm having some difficulty getting one of the boost.python tutorial examples working. In particular the class with a string constuctor. http://www.boost.org/doc/libs/1_37_0/libs/python/doc/tutorial/doc/html/pyth… This exact example crashes for me in Visual Studio with an exception at line 75 in <boost/python/detail/invoke.hpp>. I've read a few other forum posts and I can only assume there was something wrong with my build / config seeing as this seems like a trivial example. I am using the free boost download (http://www.boostpro.com/products/free) for VC9 and Python 2.5. I'm wondering if this is the right version of Python for that build? I couldn't find in the download any indication of what python version it's expecting, or if it evens matters. Any guidance would be much appreciated. Many thanks- Cameron -- View this message in context: http://www.nabble.com/Boost-Pro-Python-Version-tp21683370p21683370.html Sent from the Python - c++-sig mailing list archive at Nabble.com.

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bindings size
by Renato Araujo Jan. 27, 2009

Jan. 27, 2009

hi all, After some vacation I got back to my library binding. Most problems have been solved but now I got another big problem here. My current binding library is very huge compared to the wrapped C++ library (about four times). Checking the code I found that the components responsible for a great deal of the size are "class_" instantiation and ".def" functions. Without these functions my code size is about 300k and with these functions my code grows to enormous 4MB. I would like to know if there is a way to minimize the library size, some other function which I can call instead of ".def" functions, to minimize template usage, or some template call that I can transform into a function call. Anyway if there is work in progress to minimize the size of boost-python bindings I am very eager to help. BR -- Renato Araujo Oliveira Filho

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unload python extension lib (*.pyd)
by Jizhen Zhao Jan. 27, 2009

Jan. 27, 2009

Hi, All: I need to unload a C++ extension libraries in python (*.pyd files), but found many posts said Python do not have this ability when I search the web. I wonder if anyone knows if this is true or not. If that is true, is there any way to solve this problem? Thanks a lot, Jizhen

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