Mailman 3 June 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. 6, 2011

Aug. 6, 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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Problem with map_indexing_suite
by Damien Dupuis July 12, 2010

July 12, 2010

I'm trying to wrap a whole C++ that contains a lot of access to std::vector and std::map. I managed to wrap vectors but i've got problems with maps. The following simple example fails to compile with the error: error: no match for call to ‘(const boost::python::detail::specify_a_return_value_policy_to_wrap_functions_returning<X*>) (X*)‘ ==================================================== #include <boost/python.hpp> #include <boost/python/suite/indexing/vector_indexing_suite.hpp> #include <boost/python/suite/indexing/map_indexing_suite.hpp> using namespace boost::python; class X { public: X(std::string s): _s(s) {} std::string const repr() { return _s; } private: std::string _s; }; class Y { public: Y(): _vec(), _map() {}; void addToVec(X* x) { _vec.push_back(x); } void addToMap(int i, X* x) { _map[i] = x; } const std::vector<X*>& getXVec() { return _vec; } const std::map<int, X*>& getXMap() { return _map; } private: std::vector<X*> _vec; std::map<int, X*> _map; }; BOOST_PYTHON_MODULE(pyTEST) { class_<X, X*>("X", init<std::string>()) .def("__repr__", &X::repr) ; class_<std::vector<X*> >("XVec") .def(vector_indexing_suite<std::vector<X*>, true>()) ; class_<std::map<int, X*> >("XMap") .def(map_indexing_suite<std::map<int, X*>, true>()) ; class_<Y>("Y", init<>()) .def("addToVec", &Y::addToVec) .def("addToMap", &Y::addToMap) .def("getXVec" , &Y::getXVec , return_internal_reference<>()) .def("getXMap" , &Y::getXMap , return_internal_reference<>()) ; } ==================================================== I tried to use boost::shared_ptr<X> instead of X* in this small example and it works, but I would like not to have to correct all my existing C++ code to use boost::shared_ptr. And since it works well with std::vector<X*>, I think it should work with maps. Some google search make me think I should add a return_value_policy to the __getitem__ method of std::map<int, X*> class, but when I try I get the error error: address of overloaded function with no contextual type information I'm clearly doing something wrong here. Thanks for any help/advice. FYI: I'm using boost 1.42.0, with g++ 4.2.1 on snow leopard (10.6.3) ------------------------------- Damien Dupuis

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boost python and clang++
by Dane Springmeyer June 29, 2010

June 29, 2010

Anyone tried building a boost python application using clang++? I noticed this post: http://blog.llvm.org/2010/05/clang-builds-boost.html#more and gave it a shot with mapnik (mapnik.org). Compiled fine (in nearly half the time), but it appears that exception translation is not working: http://trac.mapnik.org/ticket/565 Any thoughts or ideas welcome! Dane

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Re: [C++-sig] Exposing std::list<> via Boost.Python
by Benoît Leveau June 23, 2010

June 23, 2010

> > We have a lot of C++ code using a home-grown Event<T> class template. An > > Event<T> is just a list of pointers to callback function objects. More > > precisely, an Event<T> is a std::list<unary_function<T>*>, where > > unary_function is a polymorphic function object class. Code that > > generates an event iterates through the list, dereferences each pointer > > and calls the corresponding function. > > > > I'd like python code to be able to generate these C++ events. To do that > > Event<>s need to support Python's iterable interface, which requires > > random access to the container.Unfortunately, std::list<> doesn't > > support random access. Short of copying the contents of every > > std::list<> to a std::vector<> for Python's benefit I don't see how this > > can be accomplished. > > > > Does anyone have any ideas for a simpler, more natural implementation? > > > > You don't need random access to make a python iterable at all - Python's built-in dict and set types are examples. All you need to do is define an __iter__ special function, and you should be able to do that fairly automatically using the stuff described here: > > http://www.boost.org/doc/libs/1_43_0/libs/python/doc/v2/iterator.html > Jim Bosch I often refer to this page when I want to add the __iter__ function. It clearly shows all the available options. http://wiki.python.org/moin/boost.python/iterator Add to that boost::make_transform_iterator and possibilities are endless ;)

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wrapping a reference counted class
by Nathan Cournia June 23, 2010

June 23, 2010

Hi, I'm trying to wrap the following class: class Node { public: virtual ~Node(); virtual void compute(); void incRef(); void decRef(); private: unsigned _refCount }; As you can see, the class is reference counted. In most places in my code, I pass around Node* pointers. I rarely call incRef() and decRef() to avoid overhead. I only call incRef() and decRef() in places where they are absolutely needed. For instance: void addNode(Node* n) stores a pointer to n and calls n->incRef(). Likewise: void remNode() removes its copy of the Node pointer and calls n->decRef(). Finally: Node* getNode() Returns a pointer to the Node stored by addNode(). It does _not_ call n->incRef(). Now, let's say I wrapped the three functions above with Boost.Python. I'm looking for the following reference counting behavior when doing the following in Python: 0>> x = Node() # refs = 1 1>> addNode(x) # refs = 2 2>> y = getNode() # refs = 3 3>> del x # refs = 2 4>> del y # refs = 1 5>> remNode() # refs = 0 How do I wrap Node such that I get the reference counting behavior above? I took a look at: http://wiki.python.org/moin/boost.python/PointersAndSmartPointers but at first glance it doesn't appear to be what I want. I'm not using smart pointers, instead I'm manually incrementing and decrementing the reference count. Thanks in advance for any help. nathan

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Exposing std::list<> via Boost.Python
by Phil Bass June 23, 2010

June 23, 2010

We have a lot of C++ code using a home-grown Event<T> class template. An Event<T> is just a list of pointers to callback function objects. More precisely, an Event<T> is a std::list<unary_function<T>*>, where unary_function is a polymorphic function object class. Code that generates an event iterates through the list, dereferences each pointer and calls the corresponding function. I'd like python code to be able to generate these C++ events. To do that Event<>s need to support Python's iterable interface, which requires random access to the container. Unfortunately, std::list<> doesn't support random access. Short of copying the contents of every std::list<> to a std::vector<> for Python's benefit I don't see how this can be accomplished. Does anyone have any ideas for a simpler, more natural implementation? -- Phil Bass (pab(a)isotek.co.uk) The views expressed in this e-mail/posting are those of the author and do not necessarily reflect those of Isotek Electronics Ltd.

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interfacing headle binary file library, raw pointer and buffer
by heroxbd＠gmail.com June 22, 2010

June 22, 2010

Dear all, I am trying to interface a binary file library using py++. There is a function in the library like int read(void* buffer, size_t len) which is hard to wrap. It read a piece (size len) of the file, and store it in buffer, and then return the buffer length (most likely equal to len). If I do nothing special, the py++ generated module would be like: ,---- | >>> s = "" | >>> l = 1 | >>> binary_file.read(s, l) | .... | did not match C++ signature: | (python str type could not match void*) `---- Here are what I have tried (with no success): 1. I found the keyword "opaque pointer" in boost.python and py++. My knowledge is so limited that I couldn't figure out if my case is _actually_ an opaque pointer problem, cuz all the documentation[1] for py++ and boost.python are talking about opaque return pointer, not a passed pointer. I poked around py++ to add some class policies (from the example of gmp wrapper) resulting in no change in the py++ generated boost.python code. 2. Then I tried to change the function to int read(char* buffer, size_t len) with type casting done internally in c++. Then ,---- | >>> s = "" | >>> l = 1 | >>> binary_file.read(s, l) | 1 | (the function executed successfully, with no c++ signature type mismatch) | >>> s | Segment Fault (python crash) `---- maybe it is the methodology of python that not touching "low level" mem management. I guess that's what making this problem non-trivial. I may recompile my python with debugging information an trace it with gdb to find out why it is crashing. But not yet. 3. I tried ctypes: ,---- | >>> s = ctypes.c_char_p | >>> l = 1 | >>> binary_file.read(s, l) | (c++ signature type mismatch) `---- I guess we just cannot mix ctypes with boost.python directly. Now I need to learn and try something new to solve this issue. After some web searching, I find some possiblities: 1. py++ ctypes integration[2]. It looks promising. I would like to confirm on this list if it is suited to my case. 2. write a wrapper like ,---- | struct void_p { | void * ptr | } `---- and then change all the original c++ interface from func(void * buf, ...) to func(void_p buf, ...) (there are around 6 such functions) and take care of the internal convertion by hand. But in this case the interface becomes thicker. I regard it as the last choice cuz I want to keep new c++ code minimum (hopefully all auto generated by py++). 3. I came across struct module[3] in python. It seems to suit my needs; I'm not sure. I couldn't figure out how to use it right now. 4. pyOgre might have been already solved this kind of raw memory problem. I could learn pyOgre team's example and apply their method to my case. There may be a sharp learning curve though. ... I am not sure which path I should take. I am a beginner in c++ and python and c++/python integration. The documentations and mailing list archives seems overwhelming to me. I couldn't find a fresh point to start digging into. Please give me some suggestion and advice. I am ready to learn and try and practise. Cheers! Benda footnotes: 1. http://www.boost.org/doc/libs/1_43_0/libs/python/doc/v2/opaque.html http://language-binding.net/pyplusplus/documentation/functions/call_policie… 2. http://language-binding.net/pyplusplus/documentation/ctypes/ctypes_integrat… 3. http://docs.python.org/library/struct.html -- XU Benda Research Center for Neutrino Science Tohoku University JAPAN http://www.awa.tohoku.ac.jp/~benda

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