Mailman 3 September 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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TypeError: No to_python (by-value) converter found for C++ type: class std::basic_ostream<char, struct std::char_traits<char> >
by Simon W Sept. 30, 2010

Sept. 30, 2010

Hi, Im trying to expose limited parts of std::ostream like this: { class_<std::ios_base, boost::noncopyable>("iosbase", init<const std::ios_base&>()) ; class_<std::ios, bases<std::ios_base>, boost::noncopyable>("ios", init<std::streambuf*>()) ; std::ostream&(std::ostream::*write)(const char*, std::streamsize) = &std::ostream::write; return class_<std::ostream, bases<std::ios>, boost::noncopyable>("ostream", no_init) .def("write", write , return_value_policy<copy_non_const_reference>()) ; } When I call a python function from a C++ wrapper class: virtual Uint32 serialise(const GameObject* obj, std::ostream& file) { try { if(boost::python::override f = get_override("serialise")) return f(boost::python::object(boost::python::ptr(obj)), boost::python::object(boost::python::ptr(&file))); else return ComponentSystem::serialise(obj, file); } catch(...) { PyErr_Print(); } } I get this error: *TypeError: No to_python (by-value) converter found for C++ type: class std::basic_ostream<char,struct std::char_traits<char> >* This is the python function * def serialise(self, gameobj, file): if(gameobj in self.components): file.write("HEY", 3)* What's the problem here? Is is because the ostream argument is an reference? Thanks!

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Derivation from Python str
by Willi Karel Sept. 29, 2010

Sept. 29, 2010

I'd like to derive from either Python's built-in 'str' or boost::python::str, resulting in a class that provides additional methods / member functions / attributes. The definitions of these additional methods are implemented in C++. Is there any way to achieve that? Please note that implicit conversions don't serve this goal, as methods of 'str' should be part of the derived classes set of attributes - e.g. the following Python code should be ok ('Derived' being the class derived from Python's 'str'): >>> Derived d >>> d.startswith('prefix') I see that Python's 'str' is immutable, which is acceptable for my purpose. What I tried: Including e.g. boost::python::str in the list of base classes yields a run-time error in python: boost::python::class_<Derived, boost::python::bases< boost::python::str > >("Derived") .def("foo",&Derived::foo) ; Including std::string (which is built-in-converted to Python's 'str') in the list of base classes yields a run-time assertion complaining about the base class not having been wrapped. What I'd like to achieve anyway, is derivation from Python's 'str', not std::string. Thanks for any help! Cheers, Willi.

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Read and write byte streams python<-->c++
by Simon W Sept. 29, 2010

Sept. 29, 2010

Hey, I'm trying to serialise some data. I have a c++ class: class ostream { std::ostream& stream; public: ostream(std::ostream& s) : stream(s) {} void write(const char* bytes, Uint32 count) { stream.write(bytes, count); } }; As you can see, it only wraps std::ostream. I call the python function like this: ostream stream(file); GameObject* obj = new GameObject(...); if(boost::python::override f = get_override("serialise")) return f(boost::python::object(boost::python::ptr(obj)), boost::python::object(boost::python::ptr(&stream))); Then in the python script: def serialise(self, gameobj, file): if(gameobj in self.components): b = pickle.dumps(self.components[gameobj]) # this is some testing code and dont really make sense because I don't know what to do... file.write(str(len(str(b))), 10) # try to serialise an int that tells the size of the byte-object print(len(str(b))) file.write(str(b), len(str(b))) # write the byte object return len(str(b)) + 10 # return amount of bytes we wrote First i "pickle" a python object. I convert that byte-object to a string since my write() function in c++ takes a const char*. But i'd like to pass the byte-object directly since const char* is basically a byte, right? Also, the other problem, when im about to read the serialised data I need to know the size of the previously serialised data to unpickle it. I thoght that I could to the c++ way and add a integer before the byte stream that reveal how big it is. But How can i serialise an int from python that takes up constant "byte-size" for an integer between lets say 0-10000!? Any help on this one? Thanks!

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operator in return false while operator == return true
by Simon W Sept. 24, 2010

Sept. 24, 2010

Hi, Im really scared because I fear a fundamental issue concerning the script system in my game engine. In C++, I have a class. In my class I map data to GameObject like: *class { map<GameObject*, Data> ..... }* As you see, I use the pointer as key. When I from c++, in the same class, call a python function I pass the key like this: *class::callPythonFunctions() { boost::python::get_override("callbackFunction")(boost::python::object(boost::python::ptr(gameobject))); // the variable gameobj is of type GameObject* } * When I recieve the call in python I do some checks like this: *def callbackFunction(self, gameobj): for x in self.mydict.keys(): print("Checking") print(gameobj == self.mydict) print(gameobj in self.mydict)* The above will print something like: *.... Checking True False ...* I do have a overloaded == operator. But how can I fix so that python checks for my pointer and not the PyObject* pointer ? // Simon

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bp::wrapper class returning reference type
by Charles Solar Sept. 22, 2010

Sept. 22, 2010

I have a bp::wrapper wrapping an interface for use in python. Several functions return reference types of other objects, for example: class IFoo { virtual const IBar& getBar() const = 0; } I found that to get boost python to handle this scenario correctly and eliminate any 'returning address of local variable' warnings I had to trick the result converter like so: class Foo_wrapper : IFoo, bp::wrapper< IFoo > { Bar _bar; const IBar& getBar() const { _bar = *(IBar*)this->get_override( "getBar" )(); // return *(IBar*)this->get_override( "getBar" )(); <- works as well but maybe less safe? } } I was messing with this problem for the last day and a half and this finally worked. From what I understand the method converter is tricked into returning an IBar* by the cast, then I use the copy constructor to make a concrete bar locally which is finally returned as a reference to the calling code. My first concern is if this is a 'proper' solution for this problem. I found that by just doing const IBar& getBar() const { return (IBar&)this->get_override( "getBar" )(); } I would get crashes because the object returned from get_override would be destroyed before I can copy it. IBar is abstract so most 'correct' uses will not work. If this solution is acceptable my question is how is the result converter dealing with the IBar* cast. Is it depending on me to delete the pointer? Does this solution cause massive memory leaks? Or will cleaning up the python object clean up the pointer as well? I want to implement a 'proper' solution to minimize future potential problems. Thank you

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Get parameter info of function or method
by Simon Warg Sept. 21, 2010

Sept. 21, 2010

> > Hi, I'm currently generating doc for my live boost.python classes, instances and function. But I can't find any way to retrieve the parameter info of functions and its signature because it has no __code__ attribute due to it's written I C++. Any solution to this?

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