Mailman 3 October 2009 - 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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Getting object for PyObject (reference counting)
by Murray Cumming Feb. 11, 2010

Feb. 11, 2010

I can't find any definitive documentation that tells me how I should get a boost::python::object to wrap an existing PyObject*. I guess that there's a way to do it that uses an existing reference, and a way that takes an extra reference. -- murrayc(a)murrayc.com www.murrayc.com www.openismus.com

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How do I wrap a static member function?
by James Amundson Nov. 4, 2009

Nov. 4, 2009

Hi, I have the following code: ------------------------------------------------------------------------------- #include <boost/python.hpp> #include <iostream> class Foo { public: Foo() {} ; static void doit(const char * message) { std::cout << "doing it statically: " << message << "\n"; }; void nonstatic_doit(const char *message) { std::cout << "doing it nonstatically: " << message << "\n"; }; }; using namespace boost::python; BOOST_PYTHON_MODULE(foo) { class_<Foo>("Foo",init<>()) .def("doit", &Foo::doit) .def("nonstatic_doit", &Foo::nonstatic_doit) ; } ------------------------------------------------------------------------------- When I try out my foo module, I see this: In [1]: from foo import Foo In [2]: f = Foo() In [3]: f.nonstatic_doit("hello") doing it nonstatically: hello In [4]: f.doit("hello") --------------------------------------------------------------------------- ArgumentError Traceback (most recent call last) /home/amundson/work/synergia2-devel_1_0/build/synergia2/components/foundation/<ipython console> in <module>() ArgumentError: Python argument types in Foo.doit(Foo, str) did not match C++ signature: doit(char const*) ------------------------------------------------------------------------------- How can I wrap doit? Thanks, Jim Amundson

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[python] Function objects in place of member functions
by Ravi Nov. 2, 2009

Nov. 2, 2009

Hello, If a free function 'func' has X* as its first argument, then, boost.python allows it to be bound to a member function on the python side, i.e., the following is legal: void func( X* x, arg1_t arg ) { ... } class_<X>( "X" ).def( "func", &func ); In order to use a function object in place of a free function, one must specialize/overload boost::python::detail::get_signature which, for some reason, does not account for function objects. Here's a very simple example that works: ---------------------------------------------- #include <boost/mpl/vector.hpp> struct X { int y; }; // Function object struct Z { int operator()( X *x, int z ) { return z + x->y; } }; namespace boost { namespace python { namespace detail { mpl::vector<int, X*, int> get_signature( Z&, X* ) {return mpl::vector<int, X*, int>();} }}} #include <boost/python/class.hpp> #include <boost/python/module.hpp> BOOST_PYTHON_MODULE( mft ) { boost::python::class_<X>( "X" ) .def( "z", Z() ).def_readwrite( "y", &X::y ); } ------------------------------------------------- However, note that the overload of get_signature precedes the inclusion of the boost.python headers, which is extremely inconvenient. However, if the headers are moved to their proper location as in the following, ---------------------------------------------- #include <boost/mpl/vector.hpp> #include <boost/python/class.hpp> #include <boost/python/module.hpp> struct X { int y; }; // Function object struct Z { int operator()( X *x, int z ) { return z + x->y; } }; namespace boost { namespace python { namespace detail { boost::mpl::vector<int, X*, int> get_signature( Z&, X* ) {return boost::mpl::vector<int, X*, int>();} }}} BOOST_PYTHON_MODULE( mft ) { boost::python::class_<X>( "X" ) .def( "z", Z() ).def_readwrite( "y", &X::y ); } ------------------------------------------------- the compilation fails with the following error message (gcc 4.4.1 with boost 1.37 or 1.39): $ g++ -Wall -shared -o mft.so memft.cc -lboost_python-mt - I/usr/include/python2.6 -fPIC In file included from memft.cc:1: /usr/include/boost/python/class.hpp: In member function ‘void boost::python::class_<T, X1, X2, X3>::def_impl(T*, const char*, Fn, const Helper&, ...) [with T = X, Fn = Z, Helper = boost::python::detail::def_helper<const char*, boost::python::detail::not_specified, boost::python::detail::not_specified, boost::python::detail::not_specified>, W = X, X1 = boost::python::detail::not_specified, X2 = boost::python::detail::not_specified, X3 = boost::python::detail::not_specified]’: /usr/include/boost/python/class.hpp:235: instantiated from ‘boost::python::class_<T, X1, X2, X3>& boost::python::class_<T, X1, X2, X3>::def(const char*, F) [with F = Z, W = X, X1 = boost::python::detail::not_specified, X2 = boost::python::detail::not_specified, X3 = boost::python::detail::not_specified]’ memft.cc:16: instantiated from here /usr/include/boost/python/class.hpp:536: error: no matching function for call to ‘get_signature(Z&, X*)’ Why is the overloaded get_signature not picked up when it is declared *after* the inclusion of the headers? The reason for using function objects is to change the argument types of a member function of X as seen by python; for example, the functor would have an argument type 'double' and would then internally convert the received 'double' argument from the python side into some custom type prior to passing it to the member function of X. In other words, the functor would act as a C++ equivalent of a python decorator. Regards, Ravi

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Python converters for raw pointers: request for help
by Michele De Stefano Nov. 2, 2009

Nov. 2, 2009

Hello to everyone. I'm trying to write "from Python" converters for PETSc objects of the petsc4py package. Even if no-one of you uses petsc4py, I think you can help me, if I explain some basics. Please, be patient. I want to make converters for the PETSc Mat type. Mat is defined as below: typedef struct _p_Mat* Mat; where _p_Mat is a structure whose details are not interesting for my problem. Now, I managed to make a functioning "to Python converter". My problem is the "from Python converter". I made a test function void print_Mat(Mat m) { ... // The implementation is not interesting }; And I tried to make a "from Python converter" with the code below (please, look at it ... it's not too long and it's very simple): struct PETSc_Mat_from_Python { PETSc_Mat_from_Python() { static bool do_registration(true); if (do_registration) { boost::python::converter::registry::push_back( &convertible,&construct,boost::python::type_id<Mat>()); do_registration = false; } } static void* convertible(PyObject* obj_ptr) { // In the line below, PyPetscMat_Get takes a PyObject* as input and returns a Mat // (if it succedes) or a PETSC_NULL (if it fails). This is a function of the petsc4py C API. // The ownership of the returned Mat is not transferred (I think) if (PyPetscMat_Get(obj_ptr) == PETSC_NULL) return NULL; return obj_ptr; } static void construct(PyObject* obj_ptr, boost::python::converter::rvalue_from_python_stage1_data* data) { void* storage = ( (boost::python::converter:: rvalue_from_python_storage<Mat>*)data)->storage.bytes; data->convertible = storage; // NOTE: The instruction below does not transfer ownership, but this is not my problem, for now new (storage) Mat(PyPetscMat_Get(obj_ptr)); } }; Then, obviously ... BOOST_PYTHON_MODULE(petsc_ext) { ... some not important lines ... PETSc_Mat_from_Python(); // Registers the converter def("print_Mat",print_Mat); } The code compiles without errors. The problem is that when calling "print_Mat" from the Python shell, the interpreter gives the error: print_Mat(m) # where m was previously and correctly built from Python and it is a Python object containing a Mat Traceback (most recent call last): File "<stdin>", line 1, in ? Boost.Python.ArgumentError: Python argument types in petsc_ext.print_Mat(petsc4py.PETSc.Mat) did not match C++ signature: print_Mat(_p_Mat*) I tried also to modify "void print_Mat(Mat m)" into "void print_Mat(const Mat m)" or "void print_Mat(const Mat& m)", but the result is the same. I tried also to debug the code, but the debugger does not enter into the "convertible" method, so I guess there is something wrong that I can't see. So may be I am missing something for the process of writing a "from Python converter" for pointer arguments. Can anyone help me, please ? -- Michele De Stefano http://www.linkedin.com/in/micdestefano

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How to call reshape((M,N),order='F') ?
by Michele De Stefano Oct. 29, 2009

Oct. 29, 2009

Hello to everyone. I have this problem. Assume I'm building a to-Python converter for a 3x2 matrix type, FORTRAN storage (these are not the real dimensions of my problem, but I give these numbers only to simplify the discussion). Into the "convert" C++ method, first, I build a list with all the matrix elements (lout); then, I instantiate a boost::python::numeric::array in this way (note: I had previously used set_module_and_type("numpy","ndarray"), for using the NumPy's array): boost::python::numeric::array v(lout) Finally, I'd like to call "reshape" on this array, in this way v.attr("reshape")(make_tuple(3,2),"F"); But it does not work. It builds, but, on runtime, I obtain the error: Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: an integer is required I tried to build and re-shape a matrix entirely from Python and I discovered that, when using reshape, you are forced to give the second parameter as order = 'C' or 'F' Now the question is: is it possible to specify a named parameter from the C++ code ? If the answer is "yes", how ? Thank you in advance, Michele -- Michele De Stefano http://www.linkedin.com/in/micdestefano

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New mds-utils release (1.2.0)
by Michele De Stefano Oct. 27, 2009

Oct. 27, 2009

mds-utils 1.2.0 have been released. Release Notes: - Improved python/fileobj.hpp: now there are 3 helper file objects and they are copy-constructible. Derivation from boost::python::object has been mantained. - Added utilities for indexing support in Python extensions. - Added boost::python converters for some boost::numeric::ublas classes. ------------------- What is mds-utils ? ------------------- mds-utils is a library intended to become a collection of several C++ utilities. It makes heavy usage of the Boost C++ libraries. Release 1.2.0 contains: - a tool for detecting machine endianity. - some useful classes that allow to treat the old C FILE pointer as a C++ stream. - C++ classes that help on treating Python file objects as C++ streams. - simple utilities for indexing support in Python extensions. - new C++ to-Python and from-Python converters for some Boost uBlas objects. Project home: http://code.google.com/p/mds-utils/ -- Michele De Stefano http://www.linkedin.com/in/micdestefano http://xoomer.virgilio.it/michele_de_stefano

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function with >15 args yields get_signature error
by Eilif Mueller Oct. 26, 2009

Oct. 26, 2009

Hi, Wrapping a function f with 16 arguments: int f(int x1, int x2, int x3, int x4, int x5, int x6, int x7, int x8, int x9, int x10, int x11, int x12, int x13, int x14, int x15, int x16) { return x1; } BOOST_PYTHON_MODULE(test) { def("f",f); } yields /usr/include/boost/python/make_function.hpp: In function ‘boost::python::api::object boost::python::make_function(F) [with F = int (*)(int, int, int, int, int, int, int, int, int, int, int, int, int, int, int, int)]’: /usr/include/boost/python/def.hpp:82: instantiated from ‘boost::python::api::object boost::python::detail::make_function1(T, ...) [with T = int (*)(int, int, int, int, int, int, int, int, int, int, int, int, int, int, int, int)]’ /usr/include/boost/python/def.hpp:91: instantiated from ‘void boost::python::def(const char*, Fn) [with Fn = int (*)(int, int, int, int, int, int, int, int, int, int, int, int, int, int, int, int)]’ test_module.cpp:20: instantiated from here /usr/include/boost/python/make_function.hpp:104: error: no matching function for call to ‘get_signature(int (*&)(int, int, int, int, int, int, int, int, int, int, int, int, int, int, int, int))’ make: *** [stream.o] Error 1 whereas all is fine if that last arg "int x16" is removed. All of gcc-4.2, gcc-4.3 and gcc-4.4 seem to exhibit the same behaviour. Same effect for libboost-python1.38-dev on Ubuntu karmic and libboost-python1.35-dev on Ubuntu jaunty. I need that 16th arg and more ... about 32 args, I think. Thanks for any help you can offer. cheers, Eilif -- Jetzt kostenlos herunterladen: Internet Explorer 8 und Mozilla Firefox 3.5 - sicherer, schneller und einfacher! http://portal.gmx.net/de/go/atbrowser -- Jetzt kostenlos herunterladen: Internet Explorer 8 und Mozilla Firefox 3.5 - sicherer, schneller und einfacher! http://portal.gmx.net/de/go/atbrowser

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