Mailman 3 November 2011 - 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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Problem with importing shared library into Python
by Edgardo C. Nov. 25, 2011

Nov. 25, 2011

Hello everybody, I am having problems with importing a .so shared library I just compiled following the example giving in the book: API Design for C++ : www.apibook.com (Chapter 11) I downloaded the Boost library and I compiled it (fullw) into a subdirectory called /compilation, where I get the /include and /lib directories. No error during the compilation (Ubuntu 11.10). Then I downloaded the code from the book examples and I compiled it without errors and I get the phonebook.so in the same directory as where I launch python interpreter, but the import in python trigger this error: ImportError: /home/pablo/phonebook/phonebook.so: undefined symbol: _ZN5boost6python6detail11init_moduleEPKcPFvvE what I think is because python does not find the library. I try to play around with the LD_LIBRARY_PATH variable, ldconfig, I copied the phonebook.so library into /usr/lib and /usr/local/lib, and nothing ... I get the same error. Can anybody explain me what is the problem? thanks a lot in advance, N.B: the version of python used during the boost compilation and .cpp compilation are the same, 2.7

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Boost.Python: How do I handle object destruction of a Python-created object?
by Adam Preble Nov. 24, 2011

Nov. 24, 2011

I'm using boost 1.47 on Windows Vista, with Visual Studio 2010. My situation is something like this: 1. I have a base interface in C++ to which I've exposed a wrapper in Python. 2. In the C++ source, I have a class that contains multiple instantiations of said interface. We can call it Foo. Foo has been wrapped too. 3. In Python, I've implemented this interface. 4. I have an instance of the object floating around that I created in Python, contained within a Foo instantiate in Python. 5. The code goes out of scope, and Foo's destructor starts. Foo's destructor will try to delete its implementations of the interface. 6. Upon running into the Python implementation of the interface, we crash. Actually, with gcc in Linux I don't see anything bad happen at all. It isn't until I try this on Windows that all hell breaks loose. What I've found with my code is that this isn't Visual Studio 2010's fault. It's calling me out on something stupid that gcc/Linux let slide. I think the fundamental question is: how I can get the resource freed through Python correctly? If I let the Python class implementation go out of scope on its own, I don't see any problems. Furthermore, Foo is content on its own. It's the merging of the two that brings me problems. Particularly, the program crashes when I try to delete the Python-instantiated object. I'm not entirely surprised by this, but I have no real good way to try to tackle this problem. I don't even have good, crisp source code to show the problem yet. The code where this has happened has been running fine on Linux for awhile so I don't have an isolated case to post. I can work towards that if I've confused everybody. One last note. I did put some test print statements in the virtual destructor I had written for the interface. I do see that code does run, so I think it ultimately comes down to the memory freeing negotiated between Python and my C++ runtime.

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Boost python and boost signal
by Jay Riley Nov. 21, 2011

Nov. 21, 2011

I was wondering if it's possible to hook python functions as slots into boost::signal or boost::signal2 signals? I found an old thread that said it wasn't directly possible, but it was from 2004.

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[Boost.Python] How to adjust Python reference counts for hybrid objects?
by Per Knudsgaard Nov. 16, 2011

Nov. 16, 2011

Hi, I have run into a small problem with my understanding of Python reference counts with Python/C++ hybrid objects. I have an abstract interface called A and an associated factory interface called AFactory. I am looking to implement various A+AFactory combinations in both C++ and Python. I am using boosts intrusive smart pointers to make life a little more interesting. I have attached two files that illustrate my problem (they are a little long, sorry about that but I couldn't come up with a better example). On linux, compile the cpp file with: $ g++ foo.cpp -g -fPIC -shared -I/usr/include/python2.7 -lpython2.7 -lboost_python -o module.so Run the py file with a single argument ('crash' to produce a segfault, anything else to have it work). What am I doing? The abstract factory interface looks roughly like this (with most of the pointer stuff removed): class AFactory { public: virtual A::Ptr newA() = 0; }; A single function that returns an intrusive pointer to the A interface. I have an AFactoryWrap class that will forward the call to a python implementation. I derive it in Python as AFactoryDerived (where ADerived is the python implementation of the A interface): tmp = ADerived() class AFactoryDerived( module.AFactory ): def __init__( self ): module.AFactory.__init__( self ) def newA( self ): if( sys.argv[1] == 'crash' ): return ADerived() # segfaults else: return tmp # works I then trigger the whole thing from a simple C++ function (that I also call from python, just to add to the fun): void f2( const AFactory::Ptr &factory ) { A::Ptr a = factory->newA(); a->f(); } Get a new instance of A from the factory. Call a virtual function, implemented in Python, on it that prints "In f" on stdout. It works if the instance of ADerived is persistent (global variable) and segfaults if it is temporary (local to the newA call). That makes me suspect that the problem is with Python reference counts and that I somehow need to maintain a reference from the c++ side so it doesn't get garbage collected. The boost::python::handle<> class would seem like the way to go, except I can't seem to find any decent examples of how to use it. Am I on the right track? I would assume that the handle<> should be added to the Wrapper constructors, and the ptrRelease function enhanced to count C++ and Python references, but the syntax of creating a handle and obtaining python reference counts is escaping me. Thanks, -- Per.

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Multiple modules in a single pyd
by Olivier Voyer Nov. 15, 2011

Nov. 15, 2011

Hi everyone, Is it possible to have multiple modules linking to one single pyd file? I'm using SWIG with VS2010 and I can't find a way of doing that. Thank you, Olivier

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[Boost.Python v3] handle, object, and PyObject*
by Jim Bosch Nov. 12, 2011

Nov. 12, 2011

Boost.Python has two smart-pointer-like classes for holding PyObject*. "handle<>" is more or less a customized intrusive_ptr, with the ability to be templated on other PyObject "derived" types (like PyTypeObject). The "object" hierarchy provides a much higher-level API, and defaults to Python's None rather than a null pointer. In terms of actual usage, I see: - "object" is widely used in the public Boost.Python API, and is extremely useful there. - "handle<>" is rarely used except as a bridge to create object from PyObject*. The internal API tends to use raw PyObject* instead. - "handle<>" is almost never used with a non-default template parameter. Is there any reason why the internal API uses raw PyObject* instead of handle<>? If not, I'm inclined to start using handle<> there (or even object, for features that have become widely used like rvalue-converters). And since handle<> is almost never used as a template, I'm inclined to make it a regular class - or even just a typedef of intrusive_ptr<PyObject>. Any thoughts? Jim

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Fwd: Passing Python-derived class back into a native C++ class doesn't match the C++ signature
by Adam Preble Nov. 12, 2011

Nov. 12, 2011

I am seeing this come up in many variations, with people doing slightly different things. I haven't yet seen an example doing something in this exact progression. I apologize here because I feel like I'm repeating a topic that has come up on the list before--even just a few weeks back. Here's what I'm trying to do: 1. Expose a base class with a pure virtual method. 2. Expose an acceptor class that accepts that base class as an argument for a method. 3. Implement the base class in Python 4. Pass that implemented class to the acceptor I am using Boost 1.42. I have some source snippets. I am using the wrapper method, though without it I had the same result: class BaseTest { public: virtual int GimmeNumber() = 0; virtual ~BaseTest() {} }; class BaseTestWrap : public BaseTest, public wrapper<BaseTest> { int GimmeNumber() { return this->get_override("GimmeNumber")(); } }; class ITakeFoo { public: void DoStuff(BaseTest* test) { cout << "Whoo calling BaseTest to do stuff: " << test->GimmeNumber() << endl; } }; ... class_<BaseTestWrap, boost::noncopyable>("BaseTest") .def("GimmeNumber", pure_virtual(&BaseTest::GimmeNumber)) // I have tried &BaseTestWrap here too. Not sure what to do but it doesn't solve the issue at hand ; class_<ITakeFoo>("ITakeFoo", init<>()) .def("DoStuff", &ITakeFoo::DoStuff) ; In Python: class DerivedTest(BaseTest): def __init__(self): pass def GimmeNumber(self): return 100 dt = DerivedTest() ITF = ITakeFoo() ITF.DoStuff(dt) The DoStuff() call fails: Traceback (most recent call last): File "<stdin>", line 1, in <module> Boost.Python.ArgumentError: Python argument types in ITakeFoo.DoStuff(ITakeFoo, DerivedTest) did not match C++ signature: DoStuff(ITakeFoo {lvalue}, BaseTest*) I can appreciate there being a memory-management-related policy issue but I can't see what might have to be done. What else am I missing? I guess I should add the documentation I've found would be nice to go this last mile and show how to do this step in the Boost documentation. The wrapper stuff was fine enough but they don't see it getting called back into the native C++ code. As it stands, if I do type.mro(DerivedTest), I see: [<class '__main__.DerivedTest'>, <class 'BaseTest'>, <type 'Boost.Python.instance'>, <type 'object'>] It appears to some extent it got it.

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Python freezing
by Jay Riley Nov. 11, 2011

Nov. 11, 2011

I'm doing some testing on my C++ wrappers, and I'm hitting a point where python just freezes. The debugger stops, no exception is thrown and my program stops responding. I'm not entirely sure what code to show, so if it's not enough, let me know. Here's the python code: class HealingComponent(UseComponent): def __init__(self, FieldHealMap, BattleHealMap = None): self.FieldHealMap = FieldHealMap self.BattleHealMap = BattleHealMap UseComponent.__init__(self, "HealUseModule", True, True) def Use(self, action): print action.GetName() return False def BattleUse(self, action, field): print "BattleTest" def Clone(self): return copy.deepcopy(self) Action is defined as: class Action : public Entity { public: Action(); Action(const std::string& name, const int type = EntityTypes::ActionEntity); std::vector<ActiveAction> Users; std::vector<ActiveAction> Targets; ClonePtr Clone() const override; protected: }; and wrapped as: class_<Battle::Action, boost::shared_ptr<ActionWrap>, bases<Entity> >("Action") .def(init<>()) .def(init<const std::string&>()) .def(init<const Battle::Action&>()) .def_readwrite("Users", &Battle::Action::Users) .def_readwrite("Targets", &Battle::Action::Targets) .def("Clone", &Battle::Action::Clone, &ActionWrap::CloneDefault) .def("__copy__", &generic__copy__< ActionWrap >) .def("__deepcopy__", &generic__deepcopy__< ActionWrap >) ; Entity (stripped down) is defined as: class Entity : public Cloneable<Entity> { public: const std::string& GetName() const; virtual ClonePtr Clone() const override; bool operator==(const Entity& entity) const; bool operator!=(const Entity& entity) const; Entity& operator=(const Entity& entity); private: std::string Name; static int EntityIDCounter; int NameHash; int Type; int UID; boost::unordered_map<std::string, boost::shared_ptr<Components::Component> > ComponentCollection; }; and wrapped as: class_<Entity, boost::shared_ptr<Entity> >("Entity") .def("GetName", &Entity::GetName, boost::python::return_value_policy<boost::python::reference_existing_object>()) .def("Clone", &Entity::Clone)//, &EntityWrap::CloneDefault) .def("__eq__", &Entity::operator ==) .def("__neq__", &Entity::operator !=) .def("__copy__", &generic__copy__<Entity>) .def("__deepcopy__", &generic__deepcopy__<Entity>) ;Finally, action is passed in as follows: bool UseComponentWrap::Use(Battle::Action* action) { return call_method<bool>(self, "Use", ptr(action));//, boost::ref(Targets)); } and from my main: Battle::Action act = Battle::Action("Test"); if (healertrue != nullptr) { healertrue->Use(&act); } the program freezes on action.GetName() in the python file. In fact, it freezes on any attempt to access action's properties. If I don't attemp to access action, the fuction appears to operate correctly. With no exception to catch and no error message, I'm pretty stuck of what is causing this. It'd seem theres a problem wrapping my Action class, but I can't see any errors there. When I trace through with my debugger, GetName from Entity is definitely getting called correctly. When I trace the caller of GetName its being called from template <class RC, class F, class TC BOOST_PP_ENUM_TRAILING_PARAMS_Z(1, N, class AC)>inline PyObject* invoke(invoke_tag_<false,true>, RC const& rc, F& f, TC& tc BOOST_PP_ENUM_TRAILING_BINARY_PARAMS_Z(1, N, AC, & ac) ){ return rc( (tc().*f)(BOOST_PP_ENUM_BINARY_PARAMS_Z(1, N, ac, () BOOST_PP_INTERCEPT)) );} in invoke.hpp. Continuin the step through, it goes into to_python_indirect.hpp struct to_python_indirect{ template <class U> inline PyObject* operator()(U const& ref) const { return this->execute(const_cast<U&>(ref), is_pointer<U>()); } on this->execute, if I step over, it immediately takes me into errors.cpp catch(const boost::python::error_already_set&) { // The python error reporting has already been handled. } to be exact, I can trace the error's origin to his code segment: BOOST_PYTHON_DECL PyTypeObject* registration::get_class_object() const{ if (this->m_class_object == 0) { ::PyErr_Format( PyExc_TypeError , const_cast<char*>("No Python class registered for C++ class %s") , this->target_type.name()); throw_error_already_set(); } return this->m_class_object;}when i check this->target_type, it appears as _M_d_name = 0x00745d88 ".?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@" so it seems as though string isn't in the registry? and the error gets digested silently. This is really weird and I don't quite understand why returning a string causing a problem. Is it because it's returned as a const std::string&? I'm almost positive I've returned that type before in another program without a problem. Could there be something wrong with action? it'd seem weird I can call member functions on if it's not exposed correctly, but I really don't know. If someone can help me out I'd appreciate it. Thanks Thanks.

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