Mailman 3 July 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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Can boost_python dll be delay loaded?
by David Aldrich July 30, 2010

July 30, 2010

Hi I am working on a Windows application that uses boost_python, linked with shared libraries. I need to store the boost_python dll in a folder other than one in the usual search path (exe folder, System32, search path). I propose to do this by 'delay loading' the boost_python dll and calling SetDllDirectory() from the application. So far I haven't got this to work. I have read that some DLLs can't be loaded in this way. Does anyone have experience of delay loading boost_python? Best regards David

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docstrings not being interpreted with the correct encoding
by Rosen Diankov July 26, 2010

July 26, 2010

Hi all, I'm using epydoc to document the Boost.Python-built shared object. Everything has been going great except for one minor issue of epydoc (and probably other documentation tools) not being able to extract the correct docstring encoding (utf-8 in my case). Let A be a class and foo be its member function. Then epydoc uses the "A.foo.im_func.__module__" attribute to get the global module, for which it extracts the encoding the module has set. The problem is that A.foo.im_func is a Boost.Python.function object and does not have any '__module__' attribute. Because epydoc cannot find the __module__ attribute, it cannot get the correct encoding of the docstrings, and non-latin characters are turned into garbage. This is testing with boost python 1.40 thank you, rosen,

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dynamic linking in Linux
by Jim Bosch July 24, 2010

July 24, 2010

I've just run into the "wontfix" problem detailed here: https://svn.boost.org/trac/boost/ticket/3210 Essentially, shared information held in one module (such as RTTI stuff needed for dynamic cast) isn't available to another module, leading to segfaults. I got the impression from reading the ticket comments and the linked email threads that the best solution is to do something like this, where module "B" depends on module "A": liba.so ---- C++ objects for A and Boost.Python wrappers. a.so ------- module, linked against liba.so, just invokes wrapper generator functions defined in liba.so within a BOOST_PYTHON_MODULE block. libb.so ---- C++ objects for B and Boost.Python wrappers; linked against liba.so b.so ------- module, linked against libb.so and liba.so, just invokes wrapper generator functions defined in libb.so within a BOOST_PYTHON_MODULE block However, that's not working, and the only solution I've found is to put my modules in packages with something like the following in __init__.py: import ctypes ctypes.PyDLL("%s/_a" % tuple(__path__), ctypes.RTLD_GLOBAL) from . import _a Another similar option, using sys.setdlopenflags, seems to be less favored because the dl module needed to get the flags has been deprecated in Python itself. Is this just the current state of things? Are there any efforts underway to improve matters? Or was I on track in the first case, and I was just doing it wrong? Thanks! Jim Bosch

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Help with Jamroot file
by Filipe M. S. de Campos July 24, 2010

July 24, 2010

Hello! I'm writing a wrapper of a c++ program that uses OpenCV<http://opencv.willowgarage.com/wiki/>library. I think I have to add some information to the Jamroot file to make bjam import opencv headers and compile the wrapper successfully. But I couldn't find the right command and location in Jamroot file that I need to add it. Could somebody help me? Regards Filipe Morgado Simões de Campos

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How to derive from an abstract base class
by Lutz Maibaum July 23, 2010

July 23, 2010

Dear all, I am totally new to Boost.Python, and I am going through the tutorial to get up to speed. I apologize if this is a very obvious question. Imagine I have a base class in C++ that I want to derive from both in C++ and in Python. The following code works wonderfully well: #include <boost/python.hpp> using namespace boost::python; class Base { public: virtual int f() {return -1;} }; class Derived : public Base { public: int f() {return 1;} }; class BaseWrap : public Base, public wrapper<Base> { public: int f() { if (override f = this->get_override("f")) return f(); return Base::f(); } int default_f() {return this->Base::f();} }; int func(Base& b) { return b.f(); } BOOST_PYTHON_MODULE(foo) { class_<Base> ("Base"); class_<Derived, bases<Base> > ("Derived") .def("f", &Derived::f); class_<BaseWrap, boost::noncopyable>("Base") .def("f", &Base::f, &BaseWrap::default_f); def("func", func, "Calls the method f of its argument"); } With this code, I can do the following: >>> import foo >>> d1=foo.Derived() >>> class D(foo.Base): ... def f(self): return 2 ... >>> d2=D() >>> foo.func(d1) 1 >>> foo.func(d2) 2 So far so good. Now I would like to make Base::f a pure virtual function, and I can't get it to work. 1. Attempt: class Base { public: virtual int f() = 0; }; class Derived : public Base { public: int f() {return 1;} }; class BaseWrap : public Base, public wrapper<Base> { public: int f() {return this->get_override("f")();} }; int func(Base& b) { return b.f(); } BOOST_PYTHON_MODULE(foo) { class_<Derived, bases<Base> > ("Derived") .def("f", &Derived::f); class_<BaseWrap, boost::noncopyable>("Base") .def("f", pure_virtual(&Base::f)); def("func", func, "Calls the method f of its argument"); } This compiles, but when I try to import the resulting module I get he following error message: RuntimeError: extension class wrapper for base class Base has not been created yet This makes sense, because the Python side doesn't now about the abstract C++ class Base yet. Therefore… 2. Attempt: I change the wrapping code to the following: BOOST_PYTHON_MODULE(foo) { class_<Derived> ("Derived") .def("f", &Derived::f); class_<BaseWrap, boost::noncopyable>("Base") .def("f", pure_virtual(&Base::f)); def("func", func, "Calls the method f of its argument"); } Again this compiles, but I cannot call the c++ function func with the C++ class Derived anymore: >>> import foo >>> d1=foo.Derived() >>> foo.func(d1) Traceback (most recent call last): File "<stdin>", line 1, in <module> Boost.Python.ArgumentError: Python argument types in foo.func(Derived) did not match C++ signature: func(Base {lvalue}) Apparently the Python side doesn't know anymore that the C++ class Derived is derived from Base. The core of the problem seems to be that I cannot expose the abstract base class Base directly to Python, but only the wrapper class BaseWrap. But then C++ classes derived from Base and Python classes derived from BaseWrap do not have a common ancestor in the class hierarchy. If anyone could point me in the right direction, it would much appreciated. Best, Lutz

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Help needed with simple boost.python exception handler
by David Aldrich July 22, 2010

July 22, 2010

Hi I want to add a simple exception handler to my boost.python application. I want it to print a simple message to the console, indicating the nature of the error. I have seen: try { ... } catch ( error_already_set ) { PyErr_Print(); } But is there a better solution using a boost.python method instead of PyErr_Print() ? Or, can I do something like the following? catch ( const error_already_set& e ) { cout << e.what(); } Best regards David

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