Mailman 3 October 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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Reference count on class object and import()
by Simon W Nov. 2, 2010

Nov. 2, 2010

Hey again, I'm trying to implement a load / unload module functionallity. When I delete the module in the __main__ dict the module's reference count is still > 1. I've been trying to find if I reference it anywhere else in my code but I can't find anything! When I did a check in vc++ debugger found something. When I run this code: object obj = import(name.c_str()); *obj*'s *ob_refcnt* member is 2 when I check in the vc++ debugger. Shouldn't it be 1? After that line, I put it in the __main__ dict like: mMainNamespace[ name.c_str() ] = obj; The reference count shows 4, as expected. When I'm entering my unload() function when I want to remove the module I do like: void unload() { object t = mMainNamespace[ name.c_str() ]; // reference count in t is now 4 ? mMainNamespace[ name.c_str() ].del(); // I delete but it's not unloaded properly because it's still referenced somewhere .. } What does import() do? It must save some reference somewhere?

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Mapping RAW memory data into Python
by Marek Denis Oct. 28, 2010

Oct. 28, 2010

Hi, While I had some questions concerning accessing objects in Python, that were previously created in C++ now I'd like to know whether it's possible to get access to the raw memory from Python layer. Let's suppose I have the char* ptr pointer that points to the memory chunk with IPv4 packet. I would like to be able to read (and preferably write) data from Python layer (not via wrapped object that contains char* ptr and has some methods to write/read data), but without making any memory copies. I can use struct (even define format dynamically) in Python, but I don't know how do I pass the proper pointer from C++. If I use boost::python::object I had problems that script didn't know char type. I can use boost::python::str, return it and use in Python but I suppose it does copy data into str object, right? If not Boost, maybe basic Python C API would work? BTW. Suppose I had char* txt = "some string"; How do i create boost::python::object() that would containt the whole string? Passing *txt or txt into boost::python::object(*txt) didn't work. -- regards Marek Denis

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boost.python and distutils
by John Reid Oct. 27, 2010

Oct. 27, 2010

Hi, I need to distribute a python package that includes a boost.python extension. I've been working on Linux but I'd like the distribution to install easily on any platform with boost and python. I'm guessing distutils is the way to go. I'm not sure if the easiest way is to try to get distutils to call bjam or somehow to code all the compile and link options into the setup.py script (this seems like a headache). If I get distutils to call bjam how can the setup.py script know what the files are to install given different OSes and versions of boost? Perhaps just using a boost.build script would be easier than distutils. This is what the boost.graph python bindings do. Has anyone got any experience doing this? Thanks, John.

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Wrapping method that returns const int& (boost::python)
by Panos Oct. 25, 2010

Oct. 25, 2010

I have a simple test case: class Foo { public: const int& getX() const {return x;} void setX(const int& x_) {x = x_;} private: int x; }; BOOST_PYTHON_MODULE(module) { class_<Foo>("Foo") .def("getX", &Foo::getX) ; } The problem is that I cannot wrap getX and I get a compiler error. How is it possible to wrap getX WITHOUT changing anything in Foo? Thanks in advance! Panos Christopoulos Charitos www.ancient-ritual.com www.anki3d.org

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Delete objects, remove from dict
by Simon W Oct. 25, 2010

Oct. 25, 2010

Hey, I have a dict of the main namespace in boost::python. Now I want to delete an object from the dict to unload/delete that object dict namespace = .. extract dict from __main__ module ...; namespace["test"] = object(555); namespace.remove("test"); // <- how can I do something like this with boost python? // Simon

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Re: [C++-sig] shared_ptr and register_ptr_to_python
by Jim Bosch Oct. 25, 2010

Oct. 25, 2010

On 10/10/2010 03:58 AM, Marek Denis wrote: > On 10.10.2010 03:47, Jim Bosch wrote: >> >> Pretty much everything you need should automatically work, whether you >> use shared_ptr or raw pointers with call policies. If you've invoked >> register_ptr_to_python on all the classes you're using, > > That's what I couldn't get while reading Boost tutorial (the example > code didn't work either :( ). > Let's say I have three classes: > > class A {}; > class B : public A {}; > class C : public B {}; > > should I later just put: > register_ptr_to_python< A >(); > register_ptr_to_python< B >(); > register_ptr_to_python< C >(); > ? Actually, you want something like this: register_ptr_to_python< boost::shared_ptr<A> >(); If you want to use raw pointers, I don't think you need register_ptr_to_python (see below). > Here is the small code snippet: > > +v > boost::python::call_method<void>(callback,"addToQueue",c); > -v > > where callback is a PyObject* pointer,and 'c' is a pointer to the object. > Whenever I call this instruction, I can see that the 'c' object is being > copied (I just put some cout << "debug" << endl in the definition of the > Copy Constructor), so I assumed that Python code doesn't operate on the > object that was created in C++ module. Instead, it just operates on the > copy. > I'm actually kind of surprised about this - in other circumstances (particularly when returning values in wrapped functions by pointer), Boost.Python doesn't copy pointers or references unless you explicitly ask it to. One thing that may be worth trying: when you wrap C Python, mark it as noncopyable: class_<C,bases<B>,boost::noncopyable>("C") I'd be curious to see what happens with your call_method code snippet with that in place. In any case, if you're willing to use shared_ptr everywhere instead of raw pointers, and switch your register_ptr_to_python calls as I've shown above, I think that will also stop any copying that's going on here. There should be a way to do it with raw pointers too, but I don't see it yet (and it may not exist). Jim

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