Mailman 3 May 2010 - Cplusplus-sig

boost::python embedding error - runtime - Mac OS X - 1.38
by Igor Karpov Oct. 1, 2014

Oct. 1, 2014

Hi, I am trying to run the following program: #include <iostream> #include <Python.h> #include <boost/python.hpp> using namespace boost::python; using namespace std; int main(int argc, char** argv) { { // Using Python/C Py_Initialize(); PyObject* main_module = PyImport_ImportModule("__main__"); PyObject* globals = PyEval_GetGlobals(); PyObject* locals = PyEval_GetLocals(); PyRun_SimpleString("print 'Hello World, from Python/C!'\n"); Py_Finalize(); } { // Using boost::python Py_Initialize(); object main_module = import("__main__"); object main_namespace = main_module.attr("__dict__"); try { object ignored = exec("print 'Hello World, from boost::python!'\n", main_namespace); Py_Finalize(); } catch (error_already_set const& e) { PyErr_Print(); return 1; } } return 0; } on Linux (both x86 and x86_64), with Ubuntu's default version of Boost (1.34.1) installed, I am able to do so as expected: $ ./embed Hello World, from Python/C! Hello World, from boost::python! on Mac OS X, I get a runtime error: $ ./embed Hello World, from Python/C! Bus Error Running with gdb, this is the stack trace: Hello World, from Python/C! Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000000 0x00000000 in ?? () (gdb) where #0 0x00000000 in ?? () #1 0x00bb618f in PyEval_GetGlobals () #2 0x00bce0dd in PyImport_Import () #3 0x00bce2b0 in PyImport_ImportModule () #4 0x008127d4 in boost::python::import (name=@0xbffff4a8) at libs/python/src/import.cpp:20 #5 0x00004446 in main (argc=1, argv=0xbffff510) at embed.cc:22 For this Mac, boost version is latest (1.38) and python version is: Python 2.5.4 (r254:67917, Dec 23 2008, 14:57:27) [GCC 4.0.1 (Apple Computer, Inc. build 5363)] on darwin Is this a bug? I attached the source and the cmake file I am using to build, for convenience. Thanks, --Igor.

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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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Miscellaneous Boost.Python Utilities
by Jim Bosch July 6, 2011

July 6, 2011

In the hope that others might find them useful, and perhaps contribute some of their own, I've posted a collection of miscellaneous Boost.Python extensions I've been using at the Boost sandbox: http://svn.boost.org/svn/boost/sandbox/python_extensions Features include: - Conversions between STL containers and Boost.Range iterator ranges and Python builtins like list, tuple, and dict. - Conversions between Boost.Fusion sequences and Python tuples. - A third solution to the const shared_ptr problem (see http://language-binding.net/pyplusplus/troubleshooting_guide/shared_ptr/sha…) that isn't evil (I don't think) and doesn't involve changing the Boost.Python library itself - it simply doesn't use register_ptr_to_python to register the conversion. More info is available in the README file. Also, I'm sure many of the regulars on this list have their own similar extensions, and I'd love to see them collected in one place. If you'd like to add your collection to mine, or have a suggestion for some other place I should put my collection, please let me know. I would like to limit this collection to simple things that don't depend on non-Boost libraries, however. Jim Bosch

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How to expose to a python user defined type with to/from_python convertors?
by X Wang June 3, 2010

June 3, 2010

How do I expose my C++ type to a user defined python type? I think I could use boost python class_<> wrapper to wrap around, but if I want to use to_python/from_python convertors? Say I want to expose my C++ class(CA) to a python type(PA): C++: class CA { public: //ctors, accessors... private: std::string name_; int value_; }; Python: class PA(object): def __init__(self, name, value): self.name=name self.value=value If I use, void initializeConverters() { using namespace boost::python; to_python_converter<CA, CA_to_pA>(); } with struct CA_to_PA { static PyObject* convert(CA const& s) { printf("In C++ -> python converter?\n"); std::string name=s.name(); int value=s.value(); #if 0 static boost::python::object obj; PyObject* obj_ptr=obj.ptr(); PyObject_SetAttrString(obj_ptr, "name", PyString_FromString(name.c_str())); PyObject_SetAttrString(obj_ptr, "value", PyInt_FromLong(value)); return boost::python::incref(obj_ptr); #else return boost::python::incref( //PyInt_FromLong(1999) Py_BuildValue("s", "native string works") //Py_BuildValue("{s:i,s:i}", "abc", 123, "def", 456) ); #endif } }; How do I create a boost::python::object (or PyObject*) with "name" and "value" attributes? I could get creation and return of python native types to work, but can not get user defined types returned to the python side -- always get NoneType returned. boost::python::object C2Py() { printf("Pre assignment\n"); #if 0 boost::python::object obj(new CA("From C++ to python", 987654321)); PyObject* o=obj.ptr(); #else CA a("From C++ to python", 987654321); PyObject *o=CA_to_PA::convert(a); #endif printf("Post assignment\n"); PyObject *tmp=NULL; std::string name="No Name"; int value=-1; tmp=PyObject_GetAttrString(o, "name"); if (tmp!=NULL) name=PyString_AsString(tmp); tmp=PyObject_GetAttrString(o, "value"); if (tmp!=NULL) value=PyInt_AsLong(tmp); printf("(%s, %d)\n", name.c_str(), value); return obj; } $ python Python 2.5.1 (r251:54863, Oct 5 2007, 11:16:46) [GCC 4.1.1 20070105 (Red Hat 4.1.1-53)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import mytypes >>> pa=mytypes.C2Py() ("No Name", -1) >>>type(pa) NoneType Any help is appreciated, thanks!

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The declaration is unexposed
by vishal bayskar May 28, 2010

May 28, 2010

Hi All, I know below problem is very wired, but let me know what is going wrong. The declaration (class someClassB) is defended in file b.h in the same directory (same as a.h) but this declaration is not getting exposed. Please let me know why the declaration is not getting exposed though it is in the same directory. a.h -------- include "b.h" class someClassA { public: someClassA( someClassB const &); }; b.h -------- class someClassB { public: someClassB(); }; export.py ------------- import os import pygccxml from pyplusplus import module_builder from pyplusplus.module_builder import call_policies from pyplusplus import decl_wrappers mb=module_builder.module_builder_t(["./a.h"], ) mb.build_code_creator(module_name = 'testModule') mb.write_module('testModule.cpp') Error -------------------- vbayskar@machine03 decl]$ python export.py INFO Parsing source file "./a.h" ... INFO gccxml cmd: /usr/local/bin/gccxml -I"." "./a.h" -fxml="/tmp/tmpB13bTu.xml" INFO GCCXML version - 0.9( 1.132 ) WARNING: someClassB [class] > execution error W1040: The declaration is unexposed, but there are other > declarations, which refer to it. This could > cause "no to_python converter found" run time error. Declarations: > someClassA::someClassA(someClassB const & arg0) > [constructor] Thanks Vishal Bayskar -- View this message in context: http://old.nabble.com/The-declaration-is-unexposed-tp28692839p28692839.html Sent from the Python - c++-sig mailing list archive at Nabble.com.

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Boost.Python Problem
by alexandre monti May 26, 2010

May 26, 2010

Hello ! I've just installed Boost.Python on my iMac intel, but i've a bug. This is the code : object main_module((handle<>(borrowed(PyImport_AddModule("__main__"))))); object main_namespace = main_module.attr("__dict__"); As you can see it is very, very, very minimal and simple, and i've an exception from the second line : "TypeError: Argument name must be string, not 'str'" (please forgive my bad English, i'm French) Thanks ! _________________________________________________________________ La boîte mail NOW Génération vous permet de réunir toutes vos boîtes mail dans Hotmail ! http://www.windowslive.fr/hotmail/nowgeneration/

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No to_python (by-value) converter found for C++ type
by vishal bayskar May 25, 2010

May 25, 2010

I am facing a problem while creating python binding for some code in my application. I have created a sample program for that and attached the same to this mail. Here after the generation of python bindings when I try to use that it fails with error No to_python (by-value) converter found for C++ type: CallResult<Simple> Where as for this example code it even does not shows warning that CallResult<Simple> is unknown type, still I used sizeof and even in the generated code I could find CallResult<Simple> class. Attached tar file contains: structEx.cpp (cpp code) ex.py (python code generator script) exWithSizeOf.py (python code generator script using size of) sizeof.h include.h t.py(example python script to use the generated binding ) g++ -fpic -shared -o testModule.so -I/usr/include/python2.4/ -L/usr/lib64/ -lboost_python testModule.cpp (command for compilation) Can you please suggest what I am missing in this case. After some analysis I found, in my case python bindings generated contains line: typedef bp::class_< CallResult< Simple >, boost::noncopyable > CallResult_less__Simple__greater__exposer_t; I could not understand why boost::noncopyable is added as an extra template parameter and this seems to be be culprit in my case. I don't think my class contains object of any class which is derived from boost::noncopyable. Can you please suggest, what I am missing in this case? http://old.nabble.com/file/p28664090/structEx.tar.gz structEx.tar.gz -- View this message in context: http://old.nabble.com/No-to_python-%28by-value%29-converter-found-for-C%2B%… Sent from the Python - c++-sig mailing list archive at Nabble.com.

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automatic conversion of tuple to vector
by Nathan Cournia May 25, 2010

May 25, 2010

Hi All, The FAQ at: http://www.boost.org/doc/libs/1_43_0/libs/python/doc/v2/faq.html lists the following code as not possible with boost.python: C++: void foo(std::vector<double>& array) { for(std::size_t i=0;i<array.size();i++) { array[i] *= 2; } } Python: >>> l = [1, 2, 3] >>> foo(l) >>> print l [2, 4, 6] Basically, the desired behavior is to have a C++ function which accepts a vector in C++; accept a tuple/list when in Python. I'm not sure if the FAQ is up-to-date. Is this still not possible in boost.python? How do people generally get the behavior I outlined above? Thanks! nathan

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How to wrap reference to abstract base class to get C++ polymorphism
by Kun Hong May 25, 2010

May 25, 2010

Hi, I have a maybe entry-level question. But it really troubled me for a while. I need to wrap a C++ library which has some factory method to return references to some abstract base classes. So the implementation is hidden. If I want a python equivalent to the abstract base class reference type (so the polymorphism can work), how should I do it? Please see a very simplified example below which demonstrates what I mean. === test.cpp (wrapper and library code) #include <boost/python.hpp> using namespace boost::python; class B { public: virtual const char *getName() const = 0; }; class C : public B { public: virtual const char *getName() const { return "Class C"; } }; const B& getB() { static boost::shared_ptr<B> b(new C); return (*b.get()); } BOOST_PYTHON_MODULE(Test) { class_<B, boost::noncopyable> ("B", no_init) .def("getName", pure_virtual(&B::getName)) ; def("getB", &getB, return_value_policy<reference_existing_object>()); } === main.cpp (C++ test code) #include "test.h" #include <algorithm> #include <iostream> using namespace std; int main() { printf("%s\n", getB().getName()); return 0; } === test.py (python test code utilize the C++ extension) from Test import * print getB().getName() === end Using the above code, when I run test.py, it gives the below error: Traceback (most recent call last): File "test.py", line 3, in <module> getB().getName() RuntimeError: Pure virtual function called Then I tried changin this line def("getB", &getB, return_value_policy<reference_existing_object>()); to: def("getB", &getB, return_value_policy<copy_const_reference>()); Then when I run test.py, the error becomes: Traceback (most recent call last): File "test.py", line 3, in <module> getB().getName() TypeError: No to_python (by-value) converter found for C++ type: B What is the correct way to wrap this abstract class reference to the the polymorphic behavior? Thanks in advance. Kun

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