Mailman 3 August 2006 - Cplusplus-sig

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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C++ singleton
by Emmanuel Taurel Oct. 31, 2007

Oct. 31, 2007

Hello everybody, I am actually writing an interface to python for an existing C++ library using Boost. This library has a C++ singleton class. This class has only one constructor (with arguments) which is "protected" because it's a singleton. I am not able to build a Boost interface to this class because the compiler complains that the constructor I have given to Boost in the class_xxx constructor argument is not public (which is true) ! Therefore, my question is simple : How is it possible to interface such a class with only one constructor which is protected and a static method to create/access the object ? Thank's very much for your answer. Sincerely Emmanuel Taurel (etaurel(a)cells.es) PS : By the way, is there a searchable archive of this mailing list ?

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Exposing c++ classes with static arrays using Boost.Python and py++
by Abhi Oct. 3, 2006

Oct. 3, 2006

While running py++ on a class with a static array inside it, py++ generates Boost.Python bindings using a derived class for the original C++ class. Let me illustrate with the help of the following example: class AttributesTest { public: int staticIntArray[10]; }; Notice this class has an array inside it Running py++ generates the following code, with a wrapper class that derives from the AttributesTest class. struct AttributesTest_wrapper : AttributesTest, bp::wrapper< AttributesTest > { AttributesTest_wrapper(AttributesTest const & arg ) : AttributesTest( arg ) , bp::wrapper< AttributesTest >() {} AttributesTest_wrapper( ) : AttributesTest( ) , bp::wrapper< AttributesTest >() {} pyplusplus::containers::static_sized::array_1_t< int, 10 > pyplusplus_staticIntArray_wrapper(){ return pyplusplus::containers::static_sized::array_1_t< int, 10 >( staticIntArray ); } }; and BOOST_PYTHON_MODULE(PYPP_YodaPacketCommon){ if( true ){ typedef bp::class_< AttributesTest_wrapper > AttributesTest_exposer_t; AttributesTest_exposer_t AttributesTest_exposer = AttributesTest_exposer_t( "AttributesTest" ); bp::scope AttributesTest_scope( AttributesTest_exposer ); AttributesTest_exposer.def( bp::init< >()[bp::default_call_policies()] ); pyplusplus::containers::static_sized::register_array_1< int, 10, bp::default_call_policies >( "__array_1_int_10" ); AttributesTest_exposer.add_property( "staticIntArray" , bp::make_function( (pyplusplus::containers::static_sized::array_1_t< int, 10 > ( AttributesTest_wrapper::* )( ) )(&AttributesTest_wrapper::pyplusplus_staticIntArray_wrapper) , bp::with_custodian_and_ward_postcall< 0, 1, bp::default_call_policies >() ) );; Note that it maps the python name "AttributesTest" to the derived class AttributesTest_wrapper. Why not just keep it simple and rather than creating a derived class just map the variable "staticIntArray" via a global method, such as: .add_property( "staticIntArray" , bp::make_function( (&::someglobal_staticIntArray_wrapper) , bp::with_custodian_and_ward_postcall< 0, 1, bp::default_call_policies >() ) );; and define the someglobal_staticIntArray_wrapper method as: pyplusplus::containers::static_sized::array_1_t< int, 10 > someglobal_staticIntArray_wrapper(){ return pyplusplus::containers::static_sized::array_1_t< int, 10 >( staticIntArray ); } Is there any drawback with just mapping the array variable to a global method rather than mapping the whole class. thanks - Abhi

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custom smart pointers
by Roman Yakovenko Sept. 19, 2006

Sept. 19, 2006

Hi. I am working on some project that defines smart pointer and uses it allover the place. I have a problem for some reason I am not able to call functions that takes the smart pointer instantiation as argument. The error I get is ArgumentError: ArgumentError: Python argument types in custom_smart_ptr_classes.ref_get_value(add_x_t) did not match C++ signature: ref_get_value(my_smart_ptr_t<controllers::controller_i> {lvalue} a) Code high level: template<T> class my_smart_ptr_t{...} struct controller_i{ virtual int get_value() const = 0; }; struct add_x_t : controller_i{ int m_value; virtual int get_value( ){ return m_value + get_add_value(); } virtual int get_add_value(){ return 0; } }; int get_value( my_smar_ptr_t<controller_i> c ){ return c->get_value(); } In order to export this code, I wrote next code: namespace boost{ namespace python{ controller_i* get_pointer( my_smart_ptr_t< controller_i > const& p ) { return p.get(); } template <> struct pointee< my_smart_ptr_t< controller_i > > { typedef controller_i type; }; //same code for add_x_t class ... }} Because both classes contains virtual function I create class-wrapper for every class. Classes and function registration is pretty simple. After this I add next registration code: register_ptr_to_python< my_smart_ptr_t< controller_i > >(); register_ptr_to_python< my_smart_ptr_t< add_x_t > >(); implicitly_convertible< my_smart_ptr_t< add_x_t >, my_smart_ptr_t< controller_i > >(); Python code: import my_module add_x = my_module.add_x_t() my_module.get_value( add_x ) # raises the error I described earlier. I think, I exposed my classes "by the book". May be I am missing something? Thanks in advance. -- Roman Yakovenko C++ Python language binding http://www.language-binding.net/

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[tutorial] Auto-Overloading example bug?
by Roman Yakovenko Sept. 12, 2006

Sept. 12, 2006

Hi. I could be wrong, but it seems to me that the Boost.Python tutorials contains bug. ( http://boost.org/libs/python/doc/tutorial/doc/html/python/functions.html#py…) The compiler ( I use msvc 7.1 ) is not able to compile the code. The main reason is that it can not decide what "f" to select. I mean, it does not know what address it should pass to "def" function. The same thing occurs for BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS. It seems to me that it is right. Some thoughts. I think, that in this case( auto-overloading example ) function "def" should not take reference to function. It should be enough to pass an instance of the constructed class. Same logic could be applied on class_::def method too. -- Roman Yakovenko C++ Python language binding http://www.language-binding.net/

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Is there a way to automatically convert a smart_ptr to a held_type (try 2)
by Allen Bierbaum Sept. 12, 2006

Sept. 12, 2006

Note: I posted this message a very long time ago on this list and still haven't found a solution. Several months ago David suggested that I repost the message again to see if anyone can help out. I am finally getting back to this project so here is the repost. I am wrapping a C++ library with boost.python that has multiple types of smart ptrs for it's objects. It has a ptr<> type that holds the object and provides a ref counting interface (through and addRef()/subRef() interface). It then has a ref_ptr<> type that acts like a "standard" smart pointer by holding a ptr<> internally and calling the ref handling operations upon construction and destruction. To correctly handle the memory for the objects, I want my boost.python class wrappers for a class T to be held using ref_ptr<T>. I can do this with: class_<T, bases<...>, ref_ptr<T> >("T",...); This all works fine. I run into a problem though when I want to use wrapped method that return ptr<>'s to objects instead of a full ref_ptr<>. For example if I wrap a method like this: ptr<Base> createObject() { ... } then when I call this from boost.python it needs to figure out that it should convert the ptr<Base> to a ref_ptr<Base>. I know that I can use register_ptr_to_python<ptr<Base> > to register a to_python converter for the type, but as I understand it this will cause the python wrapper to store the C++ object using a ptr<> type internally. This won't work correctly because it will not do any memory reference counting. What I need is a way to tell boost python that anytime it needs to convert a ptr<Base> to python it should first convert it to a ref_ptr<Base> (using a standard copy constructor in ref_ptr<>) and then use this ref_ptr as the held type like normal. At first I thought that implicitly_convertible<> would help: implicitly_convertible<ptr<Base>, ref_ptr<Base> >(); But this doesn't seem to do anything for me. (this really isn't too surprising since this isn't what implicitly_convertible is for, but it seemed worth a try). Has anyone else ran into anything similar? Any ideas? Thanks, Allen

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RuntimeError: unidentifiable C++ exception
by Qun Cao Sept. 12, 2006

Sept. 12, 2006

Hi Everyone, I created a simple class wrapper like this BOOST_PYTHON_MODULE(PythonTest) { class_<MyClass,boost::noncopyable>("pMyClass", init<char const*>()); } When I try to initialize pMyClass in python, I got this error: Traceback (most recent call last): File "<stdin>", line 1, in ? RuntimeError: unidentifiable C++ exception MyClass is part of a third party GameEngine, I can successfully use it in C++. Can anyone suggest what might went wrong here? Thanks a lot, Qun

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Lost Again! :)
by Nicolas Tessore Sept. 1, 2006

Sept. 1, 2006

Hello, thanks to your helpful replies, I think I got one step closer to understanding how Py++ should work :) I built a python script that dynamically creates a header file including all the libraries from one folder. Fortunately, each class is contained in one single header called <classname>.h, so that creating the template typedefs and instantiations work fine. Now my understanding is still lacking with respect to template functions: I followed the howto-advise and call every function once for instantiation. This works, however I need to control the name that function later has in Python. At the moment I use function pointers (I could not find something like typedef), but they don't seem to make their way into the Boost.Python binding file. --- Now something from my tests: I noticed I often get a error like super(type, obj): obj must be instance or subtype of type. from a condition in decl_wrappers/calldef_wrapper.py (line 309). However, running your GUI utility for a test, this error never occurs. What is my mistake? --- Another problem arises when I try to build an example I created for my lib: I always run into 'boost::python::init' : too many template arguments errors. I had no time to dive deeper into Boost.Python, anyone up for a quick heads-up? --- This is all :D I really appreciate your efforts in helping out, and I am confident Py++ results will soon overtake Swig and pay off the time invested. Regards, N.

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boost python mingw binaries
by Jorge Vargas Sept. 1, 2006

Sept. 1, 2006

hi does anyone plans on distributing binaries for boost_python under windows? I have try to compile it myself many times and fail. Boost and Boost Jam is something new for me, the docs for boost_python are inclined to someone that knows boost and the ones of boost itself have no leads to what to do if something goes wrong. I'm not a windows dev I just want to give an alternative here so all I need is the binary since my only goal here is to make Democracy player compile with free tools on windows. so does anyone has boost python as a binary that works under mingw?

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boost:python::arg and default value
by Roman Yakovenko Sept. 1, 2006

Sept. 1, 2006

Hi. I want to resolve the issue discussed in this thread: http://thread.gmane.org/gmane.comp.python.c++/9878/focus=9881 The short version of the discussion is: class Foo; class Foo2 { friend class Foo; Foo2(Foo *f=0); }; class Foo { Foo(Foo2 *f=0); }; It is not possible to expose both Foo and Foo2 constructors with default values, without usage of some tricks. The main problem is that, when Boost.Python initializes boost::python::arg, it requires type of default value to be registered. I had some free time and took a look on the code. I think, I understand what is going on and how to fix the situation, but still need some help here and there. I see only one possible solution - to add to Boost.Python functionality, that will allow user to control argument default value conversion time. Today, the default value converted to Python during function registration. This happens in boost::python::objects::function class constructor. Solution: 1. To add classes that will define C++ to Python convert time. struct converter_base{ virtual handle<> py_value() const = 0; //const in interface is a hack, objects::function::call member function //has const modifier }; struct default_converter : converter_base{ converts value in the constructor and saves the value in a member variable py_value returns the member variable }; struct on_first_use_converter : converter_base{ saves the C++ value as member variable py_value will convert C++ value to Python on first invocation, will save the result in member variable, after this, it will always return the member variable. }; 2. Change in keyword struct. Today keyword struct keeps function default value as instance of handle<>. This should be changed. keyword struct should keep shared_ptr to coverter_base class instance or it should keep empty shared_ptr. Thus it will be possible to control C++ to Python default value conversion time from objects::function class. 3. There are few changes, that should be done to boost::python::objects::function class. This is the place I have lack of knowledge and the code is a little bit complex and fragile. More over, every additional logic, that will be added here will downgrade performance. There are few changed that should be done to the class. 1. The class should keep all keywords, that has default value converter other than default_converter. It also should save keyword position. 2. In constructor, when we register function keyword arguments, we should skip initialization of default value, for converters other than default_converter. 3. Now, the only change left is to modify function::call method. Unfortunately I can not write the working code - lack of knowledge( or sleep ). I'll be glad, if somebody can help me here. The main problem, is that some how I should pass to the function default values and I don't exactly understand how I should do that. I attached the modified files. What do you think about those changes? -- Roman Yakovenko C++ Python language binding http://www.language-binding.net/

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