Mailman 3 April 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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sendkeys method
by sam Sept. 30, 2013

Sept. 30, 2013

Hello, Is there away(method) in C/C++ programming that make the software think that someone pressed the OK button, similar to sendkeys in VBS (WshShell.SendKeys ("{Enter}")) Thank you, Sam

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Boost::Python: inheritance + optional parameters
by Sybren A. Stüvel May 14, 2012

May 14, 2012

Dear list, This is my first post here, so I'll briefly introduce myself. My name is Sybren and I'm a PhD student at the Utrecht University. We use Boost a lot in our C++-based framework, and naturally we use Boost::Python to create our Python bindings. I want to combine two "features" that are documented well separately, however so far I haven't been able to combine them. What I want to do is have a class in C++ with virtual methods and override them in a Python subclass, AND have those virtual methods use parameters with default values. In short, I want to wrap a class like this: class ExampleClass { public: virtual std::string override_me(int x, int y=0, bool z=false) { std::stringstream msg; msg << "(x=" << x << ", y=" << y << ", z=" << z << ", base implementation"; return msg.str(); } }; And be able to produce a subclass in Python like this: from cpp_module import ExampleClass class Subclass(ExampleClass): def override_me(self, *args): return ExampleClass.override_me(self, *args) + " has been overridden" Of course all in such a way that when I pass a Subclass instance to an ExampleClass parameter of C++ code, and that C++ code calls instance.override_me(1, 2), it returns "x=1, y=2, z=false, base implementation has been overridden". I can't seem to find any documentation about this, and what I find on this mailing list was posted several years ago and involves manually creating as many methods as there are optional parameters. I hope that in recent versions of Boost (I'm using 1.48 but have no problem upgrading to the latest release) there is a more useful technique. With kind regards, -- Sybren A. Stüvel http://stuvel.eu/

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Wrapping and Passing HWND with Boost.Python
by Ehsan Pi May 1, 2012

May 1, 2012

Hello, I've created a Boost.Python wrapper (using Py++) for a C++ legacy class that takes a HWND window handle in its constructor. However, after exporting the module to python when I try to use it, I get a type mismatch error. -------------------------- Here is the C++ class I'm wrapping: // File Foo.hpp // #include "Windows.h" class Foo { public: Foo( const HWND window ){} virtual ~Foo(){} virtual int Bar( int num ) { return num; } }; -------------------------- The Py++ output: INFO Parsing source file "foo.hpp" ... INFO gccxml cmd: ""c:\Program Files (x86)\gccxml 0.9\bin\gccxml.exe" -I"." "foo.hpp" -fxml="d:\temp\tmpdng3ts.xml"" INFO GCCXML version - 0.9( 1.127 ) INFO: file "generated_wrapper.cpp" - updated( 0.001607 seconds ) -------------------------- The generated wrapper: #include "boost/python.hpp" #include "foo.hpp" namespace bp = boost::python; struct Foo_wrapper : Foo, bp::wrapper< Foo > { Foo_wrapper(::HWND const window ) : Foo( window ) , bp::wrapper< Foo >(){ // constructor } virtual int Bar( int num ) { if( bp::override func_Bar = this->get_override( "Bar" ) ) return func_Bar( num ); else{ return this->Foo::Bar( num ); } } int default_Bar( int num ) { return Foo::Bar( num ); } }; BOOST_PYTHON_MODULE(MyWrapper){ { //::Foo typedef bp::class_< Foo_wrapper > Foo_exposer_t; Foo_exposer_t Foo_exposer = Foo_exposer_t( "Foo", bp::init< HWND__ *>(( bp::arg("window") )) ); bp::scope Foo_scope( Foo_exposer ); bp::implicitly_convertible< const HWND, Foo >(); { //::Foo::Bar typedef int ( ::Foo::*Bar_function_type )( int ) ; typedef int ( Foo_wrapper::*default_Bar_function_type )( int ) ; Foo_exposer.def( "Bar" , Bar_function_type(&::Foo::Bar) , default_Bar_function_type(&Foo_wrapper::default_Bar) , ( bp::arg("num") ) ); } } } -------------------------- In python I get the not-match error: >>> import MyWrapper >>> import win32gui >>> hwnd = win32gui.GetDesktopWindow() >>> foo = MyWrapper.Foo(hwnd) Traceback (most recent call last): File "<stdin>", line 1, in <module> Boost.Python.ArgumentError: Python argument types in Foo.__init__(Foo, int) did not match C++ signature: __init__(struct _object *, struct HWND__ * window) >>> How can I correct this problem to be able to pass a window's handle (from win32gui) in Python to C++ class, and interact with it? Environment: Visual Studio 2008, Boost 1.44, gcc-xml 0.9.0, py++ 1.0.0, pygccxml 1.1.0

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held type and implicitly_convertible
by Wojciech Mamrak April 30, 2012

April 30, 2012

Hello list, correct me if I am wrong, but based on what I have found in the docs, SO and few other places, when creating an object in Python and passing it to a wrapped C++ function which expects a pointer and which takes the ownership of that pointer, one should: * use auto_ptr as held type when wrapping types being passed to that function, * create a wrapper function expecting auto_ptr which calls original function and releases the auto_ptr. Additionally, if polymorphic types are to be passed, then implicitly_convertible should be used to avoid writing multiple wrapper functions for each derived type. My question is: what happens if held type of my class is auto_ptr<T>, and the (original) function expects boost::shared_ptr<T>? Does BP register a converter for these types automatically, since implicitly_convertible is not needed at all this time? Does it call shared_ptr's ctor with auto_ptr as its parameter (which calls auto_ptr's release method, causing a wrapper function to be unneeded)? Or maybe such mixing of smart pointers should be completely avoided? Thanks for help, regards

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Passing C++ object to script Python‏
by Yoann Chaumy April 30, 2012

April 30, 2012

Hi, I have created a simple C++ class, and can successfully use in my python scripts. But my aim is to create a C++ instance, and pass it to my python script. The script will modify the instance and return it to the C++ application example : //---------------- example.h ---------------- #include <iostream> #include <string> class Personage { private: std::string m_name; int m_power; public: Personage(std::string name, int power); void setPower(); }; //---------------- example.cpp ---------------- #include "example.h" #include <Python.h> using namespace std;Personage::Personage(string name, int power) { m_name = name; m_power = power; } void Personage::setPower(int power) { m_power = power; } so, what should I do in the main to send an instance Personage to the script Python ? Any help would be appreciated

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weak_ptr to this in C++ classes extended from python
by Holger Brandsmeier April 27, 2012

April 27, 2012

Dear list, how is it possible to have a class in C++ that can be extended from python and that stores a weak_ptr to itself? The reason why I want to do this: - using a weak_ptr to itself does not introduce a memory leak. - from a C++-member of that class I can call other functions that expect a shared_ptr<>, in that case I convert the weak_ptr to a shared_ptr and all the memory management works nicely. The way I would suspect this to work is: struct I { void setThisRCP(boost::shared_ptr<I> ptr) { thisRCP = ptr; } boost::shared_ptr<I> getThisRCP() const { return thisRCP.lock(); } boost::weak_ptr<I> thisRCP; }; Then I export this class to C++ and in python I would do: class IDer(I): def __init__(self): I.__init__(self) self.setThisRCP(self) And I would suspect that I can use that class now in C++ and in particular calling getThisRCP() from C++ returns a valid shared pointer. However, immediately after the call of `self.setThisRCP(self)` the weak_ptr is already invalid and getThisRCP returns an shared pointer to Null (None in python). Attached to this message is a very simple example that demonstrates how this failes for the above implementation, the ouptu for the snipped: print '\ntestcase for thisRCP as from python extended class:' i = IDer() assert i.getThisRCP() is not None fails the assertion. However if I do the equivalent to IDer purely in C++ (which is not really an option) then everything works (see attachment) with the putput testcase for thisRCP as set from C++: 42 destructor for J called ... I suspect that the error comes from the fact that boost python create as temporary shared_ptr that is passes to setThisRCP() which is not the shared pointer that actually holds the instance of IDer in python (is it actually hold as a shared_ptr?). Do you have any proposal of how I can implement the above pattern with boost python? Or is this completly impossible at the moment? I also reported this issue before "storing weak_ptr to this in classes extended from python" but at that time I wasn't using shared_ptr and now I really suffer from the memory leak that was introduced by my workaround which was to store the thisRCP as a "shared_ptr" and I really need to fix that now. So here is a small little example that does not depend on any other parts of my library. -Holger

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No automatic upcasting with std::shared_ptr in function calls?
by Václav Šmilauer April 24, 2012

April 24, 2012

Hello, I have a sample hierarchy of polymorphic classes (A from which B inherits). One of them (A1, B1) is managed with boost::shared_ptr, the other one (A2, B2) via std::shared_ptr (I defined the get_pointer template for std::shared_ptr). When I call f1(boost::shared_ptr<A1>) with an object B1 from python, it is correctly upcast to the pointer to its base class and the c++ function is called. When I call f2(std::shared_ptr<A2>) with B2 argument from python, no upcasting takes place and I get Boost.Python.Argument error. The code is here: foo.cpp: #include<boost/shared_ptr.hpp> /// make boost::python understand std::shared_ptr #include<memory> namespace boost { template<class T> T* get_pointer(std::shared_ptr<T> p){ return p.get(); } } // define a hierarchy struct A1{ virtual ~A1(){} }; struct B1: public A1{ virtual ~B1(){} }; void f1(boost::shared_ptr<A1> ptr){ std::cerr<<"f1()"<<std::endl; } struct A2{ virtual ~A2(){} }; struct B2: public A2{ virtual ~B2(){} }; void f2(std::shared_ptr<A2> ptr){ std::cerr<<"f2()"<<std::endl; } #include<boost/python.hpp> using namespace boost::python; BOOST_PYTHON_MODULE(foo){ class_<A1,boost::shared_ptr<A1>>("A1"); class_<B1,boost::shared_ptr<B1>,bases<A1>>("B1"); def("f1",f1); class_<A2,std::shared_ptr<A2>>("A2"); class_<B2,std::shared_ptr<B2>,bases<A2>>("B2"); def("f2",f2); } compiling with (under Linux): g++ -std=c++0x foo.cpp -o foo.so -fPIC -shared -lboost_python `pkg-config python --libs --cflags` Running PYTHONPATH=. python -c "import foo; foo.f1(foo.B1()); foo.f2(foo.B2());" I obtain: f1() Traceback (most recent call last): File "<string>", line 1, in <module> Boost.Python.ArgumentError: Python argument types in foo.f2(B2) did not match C++ signature: f2(std::shared_ptr<A2>) Where is the problem? Cheers, Vaclav

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Boost Python exceptions cannot be pickled
by Faheem Mitha April 23, 2012

April 23, 2012

Hi, Briefly, when using the multiprocessing module, when exceptions are thrown, they need to be pickleable in order to propagate, since that is how multiprocessing passes information around. See http://stackoverflow.com/questions/8785899/hang-in-python-script-using-sqla… and Python bug http://bugs.python.org/issue1692335 for background. I've reported bugs http://bugs.python.org/issue13751 and http://www.sqlalchemy.org/trac/ticket/2371 and http://psycopg.lighthouseapp.com/projects/62710-psycopg/tickets/90-psycopg-… and http://bugs.python.org/issue13760 in this context. I've been reporting them as I came across them. I can produce a complete example if necessary, but I think the problem is pretty obvious. Let me know whether you require followup action from me. Specifically, do you want me to report a bug? See below the traceback I just ran into. Please CC me on all replies. Thanks. Regards, Faheem ******************************************************************* Process PoolWorker-1: Traceback (most recent call last): File "/usr/lib/python2.6/multiprocessing/process.py", line 232, in _bootstrap Process PoolWorker-2: Traceback (most recent call last): File "/usr/lib/python2.6/multiprocessing/process.py", line 232, in _bootstrap self.run() File "/usr/lib/python2.6/multiprocessing/process.py", line 88, in run self._target(*self._args, **self._kwargs) File "/usr/lib/python2.6/multiprocessing/pool.py", line 71, in worker self.run() File "/usr/lib/python2.6/multiprocessing/process.py", line 88, in run self._target(*self._args, **self._kwargs) File "/usr/lib/python2.6/multiprocessing/pool.py", line 71, in worker put((job, i, result)) File "/usr/lib/python2.6/multiprocessing/queues.py", line 366, in put put((job, i, result)) File "/usr/lib/python2.6/multiprocessing/queues.py", line 366, in put return send(obj) PicklingError: Can't pickle <class 'Boost.Python.ArgumentError'>: import of module Boost.Python failed return send(obj) PicklingError: Can't pickle <class 'Boost.Python.ArgumentError'>: import of module Boost.Python failed

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boost python writing converters for list to std::vector<T>
by Helfer Thomas April 23, 2012

April 23, 2012

Hi, using http://misspent.wordpress.com/2009/09/27/how-to-write-boost-python-converte…, I tried to write a converter for list to std::vector<T> (In the example, T will be double). The code (see converter.cxx) I wrote is still in early stage of development (no check) but compiles fine on ubuntu oneiric with boost python 1.46. I used it to create an std module. However, a simple test (see test.py) does not work as exepted. Did I misunderstood something or does boost have a special treatment for the list object which bypasses converters ? Thanks for any help, Sincerly, Helfer THomas

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