Mailman 3 June 2007 - Cplusplus-sig

[c++-sig] How does C++ cooperate with python array?
by 甜瓜 June 6, 2007

June 6, 2007

I'm sure it is a newbie question. ^_^ In my python program, it will generate a very big array stored in array.array. The data processing is time consuming. So I want to move it into C++, and return the result array back to python. Could you give me a related example by using Boost.Python library? It may like this: ============ # python code ar = array(...) ret = func(ar) # call a Boost.Python exported funtion which accepts a array.array parameter. ... # C++ code array func(array& ar) // just simple array.array, not numpy.array { ... //return array } BOOST_PYTHON_MODULE() {...} ============ Another concern is about the memory management. If I create a new array in C++ part, who will take charge of memory release? And, is there any implicit data-copying on the way that the array is passed between C++ and python? Due to the size of the array is very large, any unnecessary copy will lead to poor performance. Is there anything I should pay attention to when using Boost.Python? Thank you. -- ShenLei

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Re: [C++-sig] Boost Python: Howto wrap "out" arguments of a methode
by David Abrahams June 6, 2007

June 6, 2007

on Mon Jun 04 2007, Alexander Eisenhuth <newsuser-AT-stacom-software.de> wrote: > How to wrap methode Get with Boost.Python? First, I suggest you take your question to the C++-sig (http://www.boost.org/more/mailing_lists.htm#cplussig). > > class MyClass { > public: > MyClass(); > > void GetX(double &pos_x); > [...] > > > I'v tried it with: > > .def( > "GetX" > , &::MyClass::GetX > , bp::arg("") > , bp::return_value_policy<bp::return_arg<1>() >() > > But when I try it in python: > > Boost.Python.ArgumentError: Python argument types in > MyClass.GetX(MyClass, int) > did not match C++ signature: > GetX(class MyClass::LedPosition_C {lvalue}, int {lvalue} ) > > Any ideas? return_value_policy is only good for telling Boost.Python how to handle the actual (non-void) return value of your C++ function. In your case, create a thin wrapper function: double GetX2(MyClass& self, double pos_x) { self.GetX(pos_x); return pos_x; } and wrap that instead of GetX: .def("GetX", GetX2) -- Dave Abrahams Boost Consulting http://www.boost-consulting.com

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question about timer
by Aljaz June 4, 2007

June 4, 2007

Hello I have one boost::asio::deadline_timer object in my application.. Lets say I call/set it two times at once (the first time it expires after 6 seconds, and the second time after 10 seconds).. Now it will only expire after 10 seconds (because I have 'overwriten' the settings). In case that scenario happens, should I cancel the timer before setting it to new expire time or I can just set new timer values without calling cancel? Thanks for help Best regards A

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using extract with embedded boost::python
by Simon Pickles June 4, 2007

June 4, 2007

Hi, I am getting an error when I run example code like this: // Retrieve the main module. /* object main = import("__main__"); // Retrieve the main module's namespace object global(main.attr("__dict__")); // Define greet function in Python. object result = exec( "def greet(self): \n" " return 'Hello from Python!' \n", global, global); // Create a reference to it. object greet = global["greet"]; // Call it. std::string message = extract<std::string>(greet()); It gives error_already_set, which I catch, but then it crashes on shutdown during garbage collection. The extract line is causing the crash. Strangely this works: object main_module(( handle<>(borrowed(PyImport_AddModule("__main__"))))); object main_namespace = main_module.attr("__dict__"); handle<> ignored((PyRun_String( "import myPython" ))); int five_squared = extract<int>(main_namespace["result"]); g_log->Log( "%d\n", five_squared ); Can anyone demystify the difference to a boost:python newbie? Thanks Simon http://www.simonpickles.com --- http://www.squirtualreality.com _________________________________________________________________ Could you be the guest MSN Movies presenter? Click Here to Audition http://www.lightscameraaudition.co.uk

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Boost.Python std::cerr segfault when built with -lGL
by Gazihan Alankus June 3, 2007

June 3, 2007

Hello, I'm using Boost.Python to create a python library. When I use -lGL in my linker flags, the first string I send to std::cerr results in an exception. When I leave -lGL out, everything is fine and std::cerr works with no problems. I get this problem when I add -lGL to the simplest Boost.Python sample program that has nothing to do with OpenGL. Any ideas? Does anybody else see this behavior? I'm on Gentoo Linux, using gcc 4.1.1, Python 2.4 and Boost 1.33. I tried Python 2.3 too and it's the same. -Gazi

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extract
by Sean Ross-Ross June 2, 2007

June 2, 2007

hi, How do I write multiple to_python conversions? Say I have an boost::python::object and I call extract<somthing>, where the object could be a "c++ somthing class" or a Python dictionary Thanks

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Documentation patch
by Nikolay Mladenov June 1, 2007

June 1, 2007

Hello, I have a docstring related patch which I would like to submit. It outputs nice python signatures with every function, condensing the overloads and displaying the default parameter values. This is how the output of help looks >>> help(ugui.AngleField.value) Help on method value: value(...) unbound sitius.ugui.AngleField method value( (AngleField)self) -> Angle : returns the field's value value( (AngleField)self, (Angle)angle [, (bool)invoke_callback=False]) -> AngleField : Sets the value of the field and optionally invokes the activate callback Here is the summary of changes that I have. 1. added "PyTypeObject* converter::registration::expected_from_python_class_object() const" method used to find a python class that is convertible to a given parameter type 2 added type_info member to the signature_element to allow using the method of 1 3. added member template <class Sig> struct extract_return_type{ typename type; }; to every call policy class. for the default_call_policies class for example it is: template <class Sig> struct extract_return_type { typedef BOOST_DEDUCED_TYPENAME mpl::front<Sig>::type type; }; but for return_arg it is: template <class Sig> struct extract_return_type{ typedef BOOST_DEDUCED_TYPENAME mpl::at_c<Sig, arg_pos>::type type; }; 4. added to py_function: virtual python::detail::signature_element const& get_return_type() const {return signature()[0];} and overloaded it for the policy based py_functions 5. *HACK* made the lvalue_from_python_chain::convert(0) and rvalue_from_python_chain::convertible(0) to return PyTypeObject *( the python type they expect or 0) and used it in the implementation of 1 5 is dangerous because it will crash if someone registers lvalue_from_python_chain::convert and rvalue_from_python_chain::convertible directly with the expectation that the parameter is non zero a cleaner way would be to add another member to rvalue_from_python_chain and lvalue_from_python_chain to return their PyTypeObject expectation. 6. added a new class function_doc_signature_generator which uses 1-5 to generate python style signatures. Is there interest for this patch, and What is the best cvs diff format for submiting patch? Regards, Nikolay Mladenov Sitius Automation

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Exception using boost::python and PyRun_file
by Simon Pickles June 1, 2007

June 1, 2007

Hi, [newbie alert] I am trying to embed python in c++ with boost::python. I'm using MSVC++ 2005 Express Boost 1.34 Python 2.52 Unfortunately, I've come unstuck already. Here's my code object main_module( ( handle<>( borrowed( PyImport_AddModule( "__main__" ) ) ) ) ); object main_namespace = main_module.attr("__dict__"); FILE* myPython = fopen( "myPython.py", "r" ); handle<> ignored( ( PyRun_File( myPython, "myPython.py", Py_file_input, main_namespace.ptr(), main_namespace.ptr() ) ) ); fclose( myPython ); and heres the exception: First-chance exception at 0x7c918fea in Server 20070601.exe: 0xC0000005: Access violation writing location 0x00000010. Unhandled exception at 0x7c918fea in Server 20070601.exe: 0xC0000005: Access violation writing location 0x00000010. What am I doing wrong? must be something simple :) Thanks! Simon http://www.simonpickles.com --- http://www.squirtualreality.com _________________________________________________________________ Play your part in making history - Email Britain! http://www.emailbritain.co.uk/

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using boost.python with boost-build v2
by Fred Jendrzejewski June 1, 2007

June 1, 2007

Hello, if i want to built the hello.cpp example from the tutorial i get the warning, that it is impossible to find a Jamfile or a project-jam.root. Because all the problems seems to be a lil bit strange, i will describe my configuration as good as possible: the boost-built directory is: /usr/share/boost-build and in the tools/ directory there is no build sub-directory the bjam is in : /usr/bin i have python2.5 bjam --version gives me: Boost.Build V2 (Milestone 11) Boost.Jam 03.1.13 the directory where i copied the hello.cpp, Jamrules, the Jamfile and the boost-build.jam is ~/Boost the hello.cpp is like before. the Jamfile is that: project hello : requirements <library>/boost/python//boost_python : build_dir ~/Boost/ ; python-extension hello: hello.cpp ; the jamrules: path-global BOOST_ROOT : /usr/include/ ; project boost : $(BOOST_ROOT) ; the boost-build.jam: boost-build /usr/share/boost-build/tools ; the user-config.jam are copied in the ~/ and there you can find: import toolset : using ; using gcc ; using python : 2.5 ; Properbly i am overlooking something, but i found no solution until now. Knid Regards, Fred Jendrzejewski

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