Mailman 3 August 2005 - Cplusplus-sig

Boost.Python embedded doubt
by Eric Jardim Aug. 31, 2005

Aug. 31, 2005

Hi, For QtDesigner integration, I need to embedded Python extended classes exposed back to C++. So I started with the tutorial and the Boost.Pythontest example. The test is ok. Then I changed the example to my needs, and tryed to load the Qt module. The program compile and run, but output: Traceback (most recent call last): File "<string>", line 1, in ? File "/u/cwd7/devel/boost/python-qt4-0.0.3rc1/Qt/__init__.py", line 8, in ? import dl ImportError: /g0dv/Bin/Linux/python/lib/python2.3/lib-dynload/dl.so: undefined symbol: _Py_NoneStruct This error happens inside the PyRun_String function. I have commented the line of the "ld" module import, and it complain about another symbol. It does not look like a "dl" problem, but a linking problem. Reading the tutorial, http://www.boost.org/libs/python/doc/tutorial/doc/html/python/embedding.htm it says: "To be able to use embedding in your programs, they have to be linked to both Boost.Python's and Python's static link library." Is it really necessary to both the libs be static? I then (curiously) tried to link with the boost_python library dynamically and it complained about another (thrid Py~) symbol. I am building this app with Qt "qmake". I do not use bjam, because I need specific precompiling for Qt (easyly done by qmake). But this should not be so complex, shoud it? I am just using simple: >>> -L/path/to/python/lib/python2.3/config -lpython2.3 -L/path/to/boost/lib -lboost_python-static -lutil Am I missing something? Do I have to do anything else? The code I am trying is: > using namespace boost::python; > > object main_module(( > handle<>(borrowed(PyImport_AddModule("__main__"))))); > > object main_namespace = main_module.attr("__dict__"); > > // Define the derived class in Python. > // (You'll normally want to put this in a .py file.) > python::handle<> result( > PyRun_String( > "import Qt\n" > "from Qt.Gui import QPushButton\n" > "print QPushButton\n", > Py_file_input, main_namespace.ptr(), main_namespace.ptr()) > ); > // Result is not needed > result.reset(); > I also call PyInitialize first. Thanks for any help, [Eric Jardim]

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Re: [C++-sig] Boost.Python and slightly more tricky inheritance
by David Abrahams Aug. 29, 2005

Aug. 29, 2005

Vladimir Pozdyayev <ardatur(a)mail.ru> writes: > Greetings. Hi! The C++-sig is usually a better place for Boost.Python-related posts (http://www.boost.org/more/mailing_lists.htm#cplussig). > 1. First, about a bug (Boost 1.33.0, MSVC 7.1): > > After exporting > void test1( const char * ) { } > void test2( std::string ) { } > we get an assertion failure _BLOCK_TYPE_IS_VALID( ... ) on > std::strings longer than a dozen of characters: > test1( 'hello' ) # OK > test2( 'hello' ) # OK > test1( 'how do you do, tell me please' ) # OK > test2( 'how do you do, tell me please' ) # failure And you think this is a bug in Boost code? Can you post a reproducible test case? I bet you didn't use Boost.Build to create your extension module, as recommended in the Boost.Python documentation. You probably are linking with multiple copies of the runtime. > 2a. From `Exposing Classes' tutorial section: > > "If Base is polymorphic, Derived objects which have been passed to > Python via a pointer or reference to Base can be passed where a > pointer or reference to Derived is expected." > > Now, that's a great feature, but I couldn't help noticing that what > Boost.Python actually does, is even more useful: not only such > pointers can be passed instead of Derived ones, but their Python > counterparts _are_ fully qualified Derived representations, with all > the methods and everything. Probably worth mentioning in dox that > way. I think I would say something slightly different, but it's a good point. Joel? In fact, it will work as long as the actual dynamic type of the object has been exposed to Python. However, if the type is something derived from Derived, Boost.Python may not be able to determine the most-derived type that's been exposed. > 2b. Now, suppose we have one more derived class: > > class Base { ... }; > class Derived: public Base { ... }; > class HiddenImplementation: public Derived { ... }; > > with Derived being no more than an interface. Naturally, we don't want > to export HiddenImplementation to Python, but still want to retain > automatic conversions from Base* to Derived* whenever > pointer to HiddenImplementation object is passed to Python. > > Any way to do this? Without hack-ins? Not without a hack, no. But the hack might be simple: #include <boost/python/object/inheritance.hpp> // non-public implementation details ... boost::python::object::register_conversion<Derived,HiddenImplementation>(); boost::python::object::register_conversion<HiddenImplementation,Derived>(); > I was able to trick the system by defining the fake empty > implemetation class > class HiddenImplementation: public Derived { }; > right before the BOOST_PYTHON_MODULE and exporting it out there, but > this kind of `solution' really annoys me. And I don't understand why > it works, either :) . Oh, and it's only a partial solution, too: we do > not have to access the real implementation class, but we still have to > export something. I don't think there's any chance of a solution that doesn't require access to the real implementation class. -- Dave Abrahams Boost Consulting www.boost-consulting.com

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boost.build help
by Stephen Henry Aug. 28, 2005

Aug. 28, 2005

Hi all, I'm attempting to get my head around Boost.build and using it to build my project. I've run into some trouble and was hoping that their was someone out their that could help me: I have a directory that looks like the following: root | --- inc | --- src in root I have a "project-root.jam" file containing "path-constant BOOST_ROOT : /home/henrys/boost". In src I have a Jamfile.v2 with the following: import python ; if [ python.configured ] { python-extension dfa : dfa.cpp : <include>${BOOST_ROOT} <include>../inc <template>${BOOST_ROOT}/libs/python/build/extensions ; } else { ECHO "Python location is not configured" } and a user-config.jam in my home directory with "using python ;" contained within it. When I'm trying to compile my extension, I cd to the src directory and type bjam --v2, but I get a long error originating in boost-build.jam:1 and ending in tools/build/v2/build/feature.jam:193 with the error: "<template> is not a valid feature name". Does anyone know what I'm doing wrong? Thanks, Stephen Henry

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Cross-module inheritance
by Eric Jardim Aug. 28, 2005

Aug. 28, 2005

Hi again, I searched google and discovered that the problem is real. Cross-module inheritance and some other things do not work with boost.python (I don't know why). Some old posts show it: http://lists.boost.org/Archives/boost/2001/07/14520.php http://lists.boost.org/Archives/boost/2001/07/14491.php And recent posts show that some guys resolved the problem (partially): http://mail.python.org/pipermail/c++-sig/2005-April/008829.html http://mail.python.org/pipermail/c++-sig/2005-April/008835.html Doing: import sys, dl sys.setdlopenflags(dl.RTLD_NOW|dl.RTLD_GLOBAL) But, I am afraid this is not a portable solution. 1 - Could anyone tell me if, at least, this solution is portable among gcc compilation, even on Windows? 2 - Does anyone suggest me to use this trick now, or should I stay with the "single-module", and wait for this issue to be solved (is it possible, given boost.python current state?) 3 - Is there any other workaround? It looks like SWIG can do it (am I right?) 4 - Should I give up everything? ( hope not ;) Thanks, [Eric Jardim]

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ANN: python-qt4-0.0.2 released
by Eric Jardim Aug. 25, 2005

Aug. 25, 2005

Salve, Want to thanks the list for the exceptional support. ---- Help wanted! "Qt4 bindings for Python using Boost.Python. The goal is to make a very pythonic API but taking advantage of the power of Qt. Another goals are: QtDesigner integration, C++ embedded Python Widgets and an extensive documentation with demos and examples." http://developer.berlios.de/projects/python-qt4/ Try it out. [Eric Jardim]

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Re: [C++-sig] using a python object that implements a c++ interface in c++
by Alexis H. Rivera-Rios Aug. 24, 2005

Aug. 24, 2005

Ralf, Adding the constructor call didn't solve the problem. I still get the exception. Thanks, Alexis Programming Tutorial: In Python: To do this, do this In Perl: To do this, do this or this or this or this... In C: To do this, do this, but be careful In C++: To do this, do this, but don't do this, be careful of this, watch out for this, and whatever you do, don't do this ____________________________________________________ Start your day with Yahoo! - make it your home page http://www.yahoo.com/r/hs

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using a python object that implements a c++ interface in c++
by Alexis H. Rivera-Rios Aug. 24, 2005

Aug. 24, 2005

Hi, I'm trying to use python to create objects that implement a given interface and passing them to c++ functions. This is what I have: --- test.h --- template <class A> class MyFactory { public: virtual ~MyFactory() {} virtual A* CreateA() const = 0; }; struct Data { int x; }; The boost::python code: // Boost Includes ============================================================== #include <boost/python.hpp> #include <boost/cstdint.hpp> // Includes ==================================================================== #include "test.h" // Using ======================================================================= using namespace boost::python; // Declarations ================================================================ namespace { typedef MyFactory<Data> Factory1; struct Factory1Wrap : MyFactory<Data>, wrapper<MyFactory<Data> > { Data* CreateA() const { //return this->get_override("CreateMissile")(); return call< Data* >(this->get_override("CreateA").ptr()); } }; }// namespace // Module ====================================================================== BOOST_PYTHON_MODULE(PysteError) { class_< Data >("Data", init< >()) .def(init< const Data& >()) .def_readwrite("x", &Data::x) ; class_< Factory1Wrap, boost::noncopyable >("Factory1", init< >()) .def("CreateA", pure_virtual(&Factory1::CreateA), return_value_policy<manage_new_object> () ) ; } The python implementation of the interface: import PysteError class PyFactory(PysteError.Factory1): def __init__(self): pass def CreateA(self): d = PysteError.Data() d.x = 1; return d factory = PyFactory(); The C++ code that tries to get the python object: // Boost Includes ============================================================== #include <boost/python.hpp> #include <boost/cstdint.hpp> #include <string> #include "test.h" using namespace boost::python; int main (void) { std::string fileName = "test.py"; std::string loadModule = "execfile('"+fileName+"')"; std::string factoryName = "factory"; object factory; Py_Initialize( ); try { object main_module(( handle<>(borrowed(PyImport_AddModule("__main__" ))))); object main_namespace = main_module.attr("__dict__"); handle<> ignored((PyRun_String( loadModule.c_str() , Py_single_input , main_namespace.ptr() , main_namespace.ptr()) )); factory = main_namespace["factory"]; //// IT FAILS HERE //// const MyFactory<Data> &ptr = extract< MyFactory<Data> >(factory); std::auto_ptr<Data> d (ptr.CreateA()); } catch(error_already_set) { PyErr_Print(); } Py_Finalize(); } I get the following error: TypeError: No registered converter was able to produce a C++ rvalue of type class MyFactory<struct Data> from this Python object of type PyFactory Can anybody please explain what does the error mean? What is the correct way to do this? Thanks, Alexis Programming Tutorial: In Python: To do this, do this In Perl: To do this, do this or this or this or this... In C: To do this, do this, but be careful In C++: To do this, do this, but don't do this, be careful of this, watch out for this, and whatever you do, don't do this __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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Return policy for operator()
by Grant Goodyear Aug. 23, 2005

Aug. 23, 2005

I have an image object that overloads operator() to handle array subscripting of the object's image data by returning a float&. How do I set the return policy for operator() in pyste? I've attached some test fragments in case anybody wants to play along at home. Thanks, Grant Goodyear -- Grant Goodyear web: http://www.grantgoodyear.org e-mail: grant(a)grantgoodyear.org

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Ublas & python
by chenu＠tiscali.fr Aug. 22, 2005

Aug. 22, 2005

Hello, I'm looking for an example on ublas (vector & matrix) integration towards python; Could you provide some info or sample code. Thanks Marc ************************ ADSL JUSQU'A 8 MEGA + 3 MOIS DE TELEPHONE GRATUIT ************************ L'ultra haut débit à 15EUR/mois seulement ! Et vous téléphonez gratuitement en France vers les postes fixes, hors numéros spéciaux pendant 3 mois. Pour profiter de cette offre exceptionnelle, cliquez ici : http://register.tiscali.fr/adsl/ (voir conditions sur le site)

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Stupid question
by Eric Jardim Aug. 22, 2005

Aug. 22, 2005

Hi, C++ "double"s are mapped to which type in Python? [Eric Jardim]

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