Mailman 3 February 2012 - 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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wrapped std::vector slice affecting items in a python list
by babak April 2, 2012

April 2, 2012

Hi, I've come across some unusual behaviour that I was hoping some one might be able to explain to me. In python I have a list and a wrapped std::vector<MyCustomType> (using the vector_indexing_suite) where the list contains the items in the vector. If I slice insert items into the vector then the items in the python list change. The attached example illustrates this. Is this behaviour expected ? I'm quite confused as to what's going on so any help clarifying this would be greatly appreciated. thanks, Babak http://boost.2283326.n4.nabble.com/file/n3738972/test.py test.py http://boost.2283326.n4.nabble.com/file/n3738972/source.cpp source.cpp -- View this message in context: http://boost.2283326.n4.nabble.com/wrapped-std-vector-slice-affecting-items… Sent from the Python - c++-sig mailing list archive at Nabble.com.

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boost python & context manager/with statement
by Avi Bahra Feb. 29, 2012

Feb. 29, 2012

Does boost python support context management using the with statement? In my case I need to manage __enter__/__exit__ on the c++ side. Could not find any examples for this in the documentation. Any help appreciated. Best regards, Ta, Avi

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throw_error_already_set and compiler warnings
by Johan Råde Feb. 29, 2012

Feb. 29, 2012

The declaration BOOST_PYTHON_DECL void throw_error_already_set(); should maybe be changed to BOOST_PYTHON_DECL BOOST_ATTRIBUTE_NORETURN void throw_error_already_set(); This will help eliminate warnings on some compilers, and will save people the trouble of writing code like int f() { ... boost::python::throw_error_already_set(); return 0; // unreachable but needed to silence compiler warning } BOOST_ATTRIBUTE_NORETURN is defined in boost/exception/detail/attribute_noreturn.hpp.

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Building Boost.Python against a debug build of Python
by Adam Preble Feb. 29, 2012

Feb. 29, 2012

I previously posted about runtime oddness when switching to a debug build of python. I figured I needed to rebuild Boost.Python. The build process is fixated on using the normal python.exe and python.lib paths, rather than python_d.exe and python_d.lib. I have put those files in my Python26 directory, and then tried to get fancy by renaming them to their release names instead. It gets mad at me . . . Creating library bin.v2\libs\python\build\msvc-10.0\release\address-model-32\architecture-x86\debug-store-database\debug-symbols-on\python-debugging-on\threading-multi\boost_python-vc100-mt-y-1_47.lib and object bin.v2\libs\python\build\msvc-10.0\release\address-model-32\architecture-x86\debug-store-database\debug-symbols-on\python-debugging-on\threading-multi\boost_python-vc100-mt-y-1_47.exp module.obj : error LNK2019: unresolved external symbol __imp__Py_InitModule4 referenced in function "struct _object * __cdecl boost::python::detail::init_module(char const *,void (__cdecl*)(void))" (?init_module@detail@python@boost@@YAPAU_object@@PBDP6AXXZ@Z) bin.v2\libs\python\build\msvc-10.0\release\address-model-32\architecture-x86\debug-store-database\debug-symbols-on\python-debugging-on\threading-multi\boost_python-vc100-mt-y-1_47.dll : fatal error LNK1120: 1 unresolved externals I'm thinking that isn't what I'm supposed to do anyways. Is there something I need to do in my build string? This is how I would do a full build. Note all the baggage I added for building Python: [FWIW I'm building Boost 1.47 with VS2010's toolchain] set INCLUDE=D:\Python26\include;D:\Python26\include\Stackless b2 --toolset=msvc-10.0 --build-type=complete stage b2 --toolset=msvc-10.0 --build-type=complete architecture=x86 address-model=32 stage b2 --toolset=msvc-10.0 --with-python --build-type=complete --debug-configuration architecture=x86 address-model=32 stage debug-symbols=on debug-store=database python-debugging=on

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Boost.Python 1.33.1 and static __doc__ properties
by Andrew Buza Feb. 28, 2012

Feb. 28, 2012

I have a set of libraries that I've been trying to build for Python 2.7 using the 1.33.1 release of Boost.Python. I've used them in the past with Python 2.4, but Py2.6 made the __doc__ property on classes read-only. Because of this change I get an AttributeError (with the message "'Boost.Python.StaticProperty' object attribute '__doc__' is read-only") when I try to import the module. There's another post to this mailing list about this issue at http://mail.python.org/pipermail/cplusplus-sig/2009-August/014747.html but it doesn't look like it was ever resolved. I've tried removing explicit docstrings from my source to see if I could avoid that but things like .def_readonly appear to add them implicitly. Updating to a newer Boost release is the obvious answer but that's extremely painful for a number of reasons, one them being a handful of patches that have been applied to the my local Boost 1.33.1 release that I'd need to port to the latest version. I'd like to modify Boost.Python 1.33.1 to avoid setting static properties and I've made a few attempts at that but I haven't been successful so far. Could someone more familiar with the code tell me if this is a reasonably simple modification and maybe point me in the right direction?

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how to override __setattr__ of an extension class
by Holger Joukl Feb. 28, 2012

Feb. 28, 2012

Hi, I'm trying to instrument a wrapped class with custom __setattr__ mechanics: .def("__setattr__", &MyExtensionClass::setattr) How can I call the base class __setattr__ from within setattr and not run into infinite recursion? I.e. the analogon in C++ to >> class Foo(object): ... def __setattr__(self, attr, value): ... print "custom __setattr__" ... object.__setattr__(self, attr, value) ... >>> foo = Foo() >>> foo.x = 23 custom __setattr__ >>> foo.x 23 >>> To actually write to my instance dict I currently do PyObject* __dict__ = PyObject_GetAttrString(m_self, const_cast<char*> ("__dict__")); PyDict_SetItemString(__dict__, name, value.ptr()); inside MyExtensionClass::setattr (where m_self is PyObj*) Is there a better way? On a sidenote, I initially thought I could wrap the __dict__ in bp::dict() to use its nice Python-like API for item assignment but this seems to always make a copy of the __dict__. I.e something like bp::dict bp_dict(__dict__); bp_dict[name] = value; won't work. Regards Holger Landesbank Baden-Wuerttemberg Anstalt des oeffentlichen Rechts Hauptsitze: Stuttgart, Karlsruhe, Mannheim, Mainz HRA 12704 Amtsgericht Stuttgart

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How to use make_default with keyword expression
by Johan Råde Feb. 27, 2012

Feb. 27, 2012

The following code works fine: using namespace boost::python; class X {}; X* make_X(int n, float f) { return new X; } BOOST_PYTHON_MODULE(Test) { class_<X>("X") .def( "__init__", make_constructor(&make_X) //,(arg("n"), arg("f") = 1.0f) ); } But if I uncomment the commented line, then the code does not compile. How do I fix that?

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Wrapping a function that takes class type, such as type_info
by Adam Preble Feb. 25, 2012

Feb. 25, 2012

I am using Boost 1.47 I have these class methods: void Remove(const std::type_info &type); void Remove(const boost::python::type_info type); I tried wrapping them both in Boost.Python: void (Entity::*Remove1)(const std::type_info&) = &Foo::Remove; void (Entity::*Remove2)(const boost::python::type_info) = & Foo::Remove; class_< Foo , boost::noncopyable, shared_ptr< Foo > >(" Foo", init<>()) ... .def("Remove", Remove1) .def("Remove", Remove2) ... (I just tried type_info of both namespaces to be comprehensive here...) It'll compile and and I'll get that Remove method fine. Except I can't seem to cram something into it when I try to actually execute the subroutine. Say I have class Bar wrapped in Python too, and I have been using it fine and dandy. How do I get Remove() to accept the type of Bar as an argument? Say: foo = Foo() foo.Remove(Bar)... foo.Remove(type(Bar))... I just can't get any love here: Traceback (most recent call last): File "<stdin>", line 1, in <module> Boost.Python.ArgumentError: Python argument types in foo.Remove(Foo, type) did not match C++ signature: Remove(class game::Entity {lvalue}, struct boost::python::type_info) Remove(class game::Entity {lvalue}, class type_info)

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test if object instance is instance of extension class in C++
by Holger Joukl Feb. 24, 2012

Feb. 24, 2012

Hi, what's the recommended way to check if an object instance is an instance of my extension class in C++ code? I'm currently doing a very ugly #define isMyExtensionClass(pyobj) (strcmp(pyobj->ob_type->tp_name, "MyExtensionClass") == 0) on PyObj* pyobj. I bet there is a better way but just can't seem to find it. Holger Landesbank Baden-Wuerttemberg Anstalt des oeffentlichen Rechts Hauptsitze: Stuttgart, Karlsruhe, Mannheim, Mainz HRA 12704 Amtsgericht Stuttgart

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