Mailman 3 March 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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Problems with boost tuples to python conversion
by Maciej Sitarz April 30, 2010

April 30, 2010

Hi, I tried to expose objects of class: typedef boost::tuple<ClassA, std::string> RegisterResult; to python. I used automatic conversion (http://www.language-binding.net/pyplusplus/troubleshooting_guide/automatic_…) but as usual I hit a wall and got unsolvable error. INFO gccxml cmd: /usr/bin/gccxml -I"." -I"/home/macieks/error_examples/boost_tuples_to_python" -I"/usr/include" -I"/usr/include/python2.4" -I"/home/macieks/boost/boost_1_42_0" "test.h" -fxml="/tmp/tmp9Kp4rg.xml" Traceback (most recent call last): File "generate.py", line 14, in ? indexing_suite_version=2 File "usr/lib/python2.4/site-packages/pyplusplus/module_builder/boost_python_builder.py", line 95, in __init__ File "usr/lib/python2.4/site-packages/pyplusplus/module_builder/boost_python_builder.py", line 138, in __parse_declarations File "usr/lib/python2.4/site-packages/pygccxml/parser/project_reader.py", line 217, in read_files File "usr/lib/python2.4/site-packages/pygccxml/parser/project_reader.py", line 242, in __parse_file_by_file File "usr/lib/python2.4/site-packages/pygccxml/parser/source_reader.py", line 206, in read_file File "usr/lib/python2.4/site-packages/pygccxml/parser/source_reader.py", line 231, in read_gccxml_file pygccxml.parser.source_reader.gccxml_runtime_error_t: Error occured while running GCC-XML: /home/macieks/boost/boost_1_42_0/boost/mpl/bool_fwd.hpp:21: sorry, unimplemented: call_expr cannot be mangled due to a defect in the C++ ABI I tried to use tuples.hpp from pyogre (it has some few lines added), but the problem is the same. I attached simple example files to this mail. Best regards -- Maciek Sitarz

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Conversion of python files to C++ ostreams
by Christopher Bruns April 15, 2010

April 15, 2010

I am trying to coax boost.python to automatically convert python files to C++ std::ostreams, for methods that take arguments of type "std::ostream&". I have made some progress, and I could use some advice on how to go further. I created a derived class of std::ostream, called FilestarOstream, which takes a std::FILE* as it constructor argument. Then I created a conversion from "python file" to the FilestarOstream class. Now my python module can automatically convert a python file to a FilestarOstream for any method that takes a "const FilestarOstream&" as an argument. Ideally I would prefer to automatically convert a python file for any method that takes a (non-const) "std::ostream&" as an argument. I have included my simplified source code below My questions: 1 - Is there an easier way to do this? Does boost.python have a built in incantation for wrapping methods that take a std::ostream reference, to take python files? 2 - Is there a way to make the type conversion work for non-const reference arguments? (see print_hello_wrapper2() below) 3 - Why does my print_hello_wrapper3() not work? It takes a const std::ostream reference argument. I can pass it a FileStarOstream, so python knows how to convert a FileStarOstream to a std::ostream. Plus python knows how to convert a python file to a const FileStarOstream reference. So why can't it convert a python file to a const ostream reference? 4 - In my FilestarOstream_from_pyfile::convertible method, is there a way to check that the object is not only a file, but that it is also writable? 5 - The PyFile_AsFile docs say "If the caller will ever use the returned FILE* object while the GIL is released it must also call the PyFile_IncUseCount() and PyFile_DecUseCount() functions described below as appropriate." What is "the GIL". If I call PyFile_IncUseCount() when I construct the FileStarOstream, when would I call the corresponding PyFile_DecUseCount()? Thanks in advance for any helpful tips. ################## //// begin test.hpp //////// #ifndef TEST_API_PYFILE_OSTREAM_H_ #define TEST_API_PYFILE_OSTREAM_H_ #include <iostream> // This is the sort of method I wish to wrap std::ostream& print_hello(std::ostream& os, int foo); // FilestarOstream is intended to aid python wrapping of methods that // take ostream& args by converting an opaque C++ FILE* to a C++ ostream. // This is just one part of the (yet unproven) task of automatically // wrapping methods that take an ostream& as an argument. class FilestarOstream : public std::ostream { public: // std::ostreams can be constructed using an std::streambuf // so the first step is to construct a specialized std::streambuf // based on a FILE* // Adapted from // http://mail.python.org/pipermail/cplusplus-sig/2002-June/000896.html class std_obuf: public std::streambuf { public: std_obuf(std::FILE* file): m_file(file) {} std::FILE* updFilestar() {return m_file;} protected: std::streambuf::int_type overflow(std::streambuf::int_type c) { return std::fputc(c, m_file) == EOF ? std::streambuf::traits_type::eof() : c; } std::FILE* m_file; }; FilestarOstream(std::FILE* fp) : buf(fp), std::ostream(&buf) {} // Default constructor uses stdout FilestarOstream() : buf(stdout), std::ostream(&buf) {} std::FILE* updFilestar() {return buf.updFilestar();} protected: std_obuf buf; }; #endif // TEST_API_PYFILE_OSTREAM_H_ //////////// end test.hpp ////////// ################### //// test.cpp /// #include "test.hpp" std::ostream& print_hello(std::ostream& os, int foo) { os << "Hello, foo = " << foo << std::endl; return os; } /// end test.cpp /// ###################### // boost.python wrapping code #include "boost/python.hpp" #include "test.hpp" namespace bp = boost::python; // Three ways of wrapping print_hello() to take a python file argument, // only one of which works: // print_hello_wrapper1() works, but I wish I did not need a wrapper at all std::ostream& print_hello_wrapper1(const FilestarOstream& os, int foo) { FilestarOstream& os_nc = const_cast<FilestarOstream&>(os); return print_hello(os_nc, foo); } // A wrapper that takes a non-const reference does not work // Boost.Python.ArgumentError ... std::ostream& print_hello_wrapper2(FilestarOstream& os, int foo) { return print_hello(os, foo); } // A wrapper that takes the a const reference to the base class, ostream, also fails // Boost.Python.ArgumentError ... std::ostream& print_hello_wrapper3(const std::ostream& os, int foo) { std::ostream& os_nc = const_cast<std::ostream&>(os); return print_hello(os_nc, foo); } // Define automatic interconversion of python file <==> FilestarOstream struct FilestarOstream_to_pyfile // untested... { static PyObject* convert(FilestarOstream& os) {return PyFile_FromFile(os.updFilestar(), "FilestarOstream", "w", NULL);} }; struct FilestarOstream_from_pyfile { FilestarOstream_from_pyfile() { bp::converter::registry::push_back( &convertible, &construct, bp::type_id<FilestarOstream>()); } static void* convertible(PyObject* obj_ptr) { if( !PyFile_Check( obj_ptr ) ) {return 0;} // TODO - is there a way to check whether file is writable also? return obj_ptr; } static void construct( PyObject* obj_ptr, bp::converter::rvalue_from_python_stage1_data* data) { // TODO - the PyFile_AsFile docs say: // "If the caller will ever use the returned FILE* object while the GIL is released it must also call the PyFile_IncUseCount() and PyFile_DecUseCount() functions described below as appropriate." std::FILE* file = PyFile_AsFile(obj_ptr); typedef bp::converter::rvalue_from_python_storage<FilestarOstream> filestarOstream_storage; void* const storage = reinterpret_cast<filestarOstream_storage*>(data)->storage.bytes; new (storage) FilestarOstream(file); data->convertible = storage; } }; BOOST_PYTHON_MODULE(test_mod){ // wrap std::ostream, so python will know how to convert FilestarOstream to ostream bp::class_< std::ostream, boost::noncopyable >( "std_ostream", bp::no_init ); { //::FilestarOstream typedef bp::class_< FilestarOstream, bp::bases< std::ostream >, boost::noncopyable > FilestarOstream_exposer_t; FilestarOstream_exposer_t FilestarOstream_exposer = FilestarOstream_exposer_t( "FilestarOstream", bp::init< std::FILE * >(( bp::arg("fp") )) ); bp::scope FilestarOstream_scope( FilestarOstream_exposer ); FilestarOstream_exposer.def( bp::init< >() ); } // wrap print_hello, using one of those wrappers defined above bp::def( "print_hello", // choose your wrapper // &print_hello, // no wrapper at all, Boost.Python.ArgumentError &print_hello_wrapper1, // OK // &print_hello_wrapper2, // non-const arg => Boost.Python.ArgumentError // &print_hello_wrapper3, // base class arg => Boost.Python.ArgumentError ( bp::arg("os"), bp::arg("foo") ), bp::return_internal_reference<2>()); // Register conversion from python file to FilestarOstream bp::to_python_converter<FilestarOstream, FilestarOstream_to_pyfile>; FilestarOstream_from_pyfile(); } // end boost.python wrapping code ##### python test program ###### import test_mod import sys # First test using explicit FilestarOstream # succeeds with all wrappers, # including unwrapped print_hello stream1 = test_mod.FilestarOstream() test_mod.print_hello(stream1, 1) # Remaining tests that use python files # only work with wrappers that take an # argument of const FilestarOstream& stream2 = sys.stdout test_mod.print_hello(stream2, 2) stream3 = open('test.txt', "w") test_mod.print_hello(stream3, 3) stream3.close() ##### end test program ####

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custom r-value converters
by Nathan Stewart April 2, 2010

April 2, 2010

I have to interface with a custom string class. In my handwritten code, I had the example from http://www.boost.org/doc/libs/1_42_0/libs/python/doc/v2/faq.html#custom_str…. I'm working with an custom string class. Actually they have a String_mgr class which derives from a String_val, and exposes the string as a property called 'val'. And py++ wraps the String_mgr as an opaque structure with a working 'val' property. But the String_mgr class in c++ supports assignment and casting, and that part doesn't work even though I have done an mb.class_('String_mgr').add_properties(exclude_accessors=False). In my application code I have numerous instances of this String_mgr. I'd like to be able to contain my interactions with the particulars of String_mgr to the one definition and not have to do an .add_property('foo', getter, setter) for each and every occurence of their String_mgr class (which are quite numerous). Can I make assignment and casting work in this way, or must I modify each and every String_mgr occurence as a property? Just in case it's not clear, I have struct ClassOne { String_mgr name; } struct ClassTwo { String_mgr description; } and I want to confine all my handling specific to the String_mgr class to one location and let the wrapping of String_mgr handle the property get/set (ClassOne, etc... are IDL generated and numerous.) I can't seem to both wrap the String_mgr class and have custom converters - I'm told I have a duplicate registration. Can I get both automatic conversion and the ability to treat this wrapped class as a property of other classes? It seems to trigger on the assignment & casting but I'm just not getting it right now.

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suppressing BOOST_PYTHON_MODULE
by Nathan Stewart March 30, 2010

March 30, 2010

Can I suppress generation of the BOOST_PYTHON_MODULE while retaining the rest of the functionality the module builder provides?

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[Py++] Registration order corner case
by Christopher Bruns March 25, 2010

March 25, 2010

Py++ has produced for me over 97,000 lines of beautiful boost.python wrapping code on my project, using less than 2500 lines of python. But I am still experiencing some minor troubles that prevent me from completing my project. Suppose I wish to wrap the following: //###### foo.h ########### struct Foo1 { struct Foo2; }; struct Foo3 : public Foo1 {}; struct Foo1::Foo2 : public Foo3 {}; then, pyplusplus generates code like this: //###### foo_module.cpp ####### #include "boost/python.hpp" #include "foo.h" namespace bp = boost::python; BOOST_PYTHON_MODULE(_foo){ bp::class_< Foo3, bp::bases< Foo1 > >( "Foo3" ); { //::Foo1 typedef bp::class_< Foo1 > Foo1_exposer_t; Foo1_exposer_t Foo1_exposer = Foo1_exposer_t( "Foo1" ); bp::scope Foo1_scope( Foo1_exposer ); bp::class_< Foo1::Foo2, bp::bases< Foo3 > >( "Foo2" ); } } When I try to use this module, "from _foo import *", I get a RuntimeError: "RuntimeError: extension class wrapper for base class struct Foo1 has not been created yet" If I then move the registration of "Foo3" to below the Foo1 block in the py++ generated code, I get a new RunTimeError: BOOST_PYTHON_MODULE(_foo){ { //::Foo1 typedef bp::class_< Foo1 > Foo1_exposer_t; Foo1_exposer_t Foo1_exposer = Foo1_exposer_t( "Foo1" ); bp::scope Foo1_scope( Foo1_exposer ); bp::class_< Foo1::Foo2, bp::bases< Foo3 > >( "Foo2" ); } bp::class_< Foo3, bp::bases< Foo1 > >( "Foo3" ); } "RuntimeError: extension class wrapper for base class struct Foo3 has not been created yet The only way to avoid the registration order problem is to register these classes to boost.python in exactly the order Foo1, Foo3, Foo2 (just like the definitions in C++). #include "boost/python.hpp" #include "foo.h" namespace bp = boost::python; BOOST_PYTHON_MODULE(_foo){ typedef bp::class_< Foo1 > Foo1_exposer_t; Foo1_exposer_t Foo1_exposer = Foo1_exposer_t( "Foo1" ); bp::class_< Foo3, bp::bases< Foo1 > >( "Foo3" ); bp::scope Foo1_scope( Foo1_exposer ); bp::class_< Foo1::Foo2, bp::bases< Foo3 > >( "Foo2" ); } Is there a way to coax pyplusplus to produce this registration order?

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examples for add_override_precall_code?
by Nathan Stewart March 25, 2010

March 25, 2010

I have pyplusplus churning out code, now I'm trying to get it to resemble what I need. I need to use add_override_precall_code, to add some thread locking to my overrides, but I can't seem to figure out how to use it from the docs. Also, I have a set of overloaded virtual functions, and previously I've had a wrapper class where the python exports rename the overloads, like so: class Connection { virtual void Callback(const Type_A&); virtual void Callback(const Type_B&); } the wrapper looked like: ConnectionWrap : Connection, wrapper<Connection> { void Callback(const Type_A& arg) { ScopedGILLock lock(m_state); // the reason I'm trying to figure out add_override_porecall_code if (override o = this->get_override("Callback_Type_A")) { o(arg); } } }; I'm getting the rest of the override as above, but setting use_overload_macro doesn't rename the overloads as I need. Any clues (since pointers are references are both 'overloaded' in this context')

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vc++ assertion error upon runtime
by hitesh dhiman March 22, 2010

March 22, 2010

Hi all, I'm trying to gain access to functions that use pointers as arguments. I have written the wrapper file that converts the arguments into pointers. The compilation works successfully, but when i try to run the code from python, it gives an assertion error: Debug Assertion Failed! Expression: Vector subscript out of range Surprisingly, this error only occurs when a particular function is called, Until that point, the code works perfectly. Could someone guide me what to do?? -- Regards, Hitesh Dhiman Electrical Engineering National University of Singapore

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