Mailman 3 October 2007 - Cplusplus-sig

Using an intrusive_ptr with a noncopyable member variable
by Don Oct. 25, 2007

Oct. 25, 2007

Hello all, Just starting to try using boost python for exposing some code I've written. Essentially I have a class Object that has a protected constructor, that is derived by various other classes. This class does its own reference counting via intrusive_ptr. Because it does its own reference counting and for thread safety I have a mutex that is entered when changing the reference count. So the header file for the Object class, with unrelated functionality stripped out is. namespace Shade { class Object { protected: Object(); public: virtual ~Object(); // Reference counting public: void incrementReferences(); void decrementReferences(); unsigned int getNumberOfReferences() const; private: /** Number of references to the Object */ unsigned int numReferences; /** * Mutex for the reference counting system. * * Assures that a pointer isn't accidently deleted or * left dangling when accessed by multiple threads. */ boost::mutex mutexRefCount; } ; /** Smart Pointer for the Object class */ typedef boost::intrusive_ptr<Object> ObjectPtr; #include "ShadeObject.inl" } void intrusive_ptr_add_ref(Shade::Object* object); void intrusive_ptr_release(Shade::Object* object); I expose it to Python using the following code BOOST_PYTHON_MODULE(Shade) { python::class_<Object, boost::noncopyable, ObjectPtr>("Object", python::no_init) // class .def's ; // Uninteresting dummy test class python::class_<DummyObject, boost::noncopyable, DummyObjectPtr, python::bases<Object> >("DummyObject"); } So in C++ if I do DummyObjectPtr test1 = DummyObject(); DummyObjectPtr test2 = test1; std::cout << test1->getNumberOfReferences() << std::endl; The console will say 2 Now if I do the same in Python test1 = DummyObject() test2 = test1 print test1.getNumberOfReferences() The console will say 1 The Object wont attempt to delete itself until both test1 and test2 are set to something else so Python must be keeping a reference count. It would just be nice to know what the total number of references are across Python and C++. Any ideas?

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Re: [C++-sig] C++-sig Digest, Vol 51, Issue 25
by Shrikant Chikhalkar Oct. 25, 2007

Oct. 25, 2007

Hi, I have also check that "py_function.py" is in the same directory. i have some doubt 1) do we need to install "py_function" module before calling multiply function from that. ( install means python -m py_function) 2) individually multiply function is working fine on python prompt. 3) I am using python2.5 headers I know some where i had make a mistake. please help me to locate that thanks Shrikant On 10/25/07, c++-sig-request(a)python.org <c++-sig-request(a)python.org> wrote: > > Send C++-sig mailing list submissions to > c++-sig(a)python.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.python.org/mailman/listinfo/c++-sig > or, via email, send a message with subject or body 'help' to > c++-sig-request(a)python.org > > You can reach the person managing the list at > c++-sig-owner(a)python.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of C++-sig digest..." > > > Today's Topics: > > 1. failed in PyImport_Import() (Shrikant Chikhalkar) > 2. Re: failed in PyImport_Import() (Gustavo Carneiro) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 25 Oct 2007 12:22:24 +0530 > From: "Shrikant Chikhalkar" <shrikantvc(a)gmail.com> > Subject: [C++-sig] failed in PyImport_Import() > To: c++-sig(a)python.org > Message-ID: > <87de5f460710242352w5b57dc4djbcfba96ccf0f3578(a)mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Hi, > > i am tring to call python function from 'C' program. i get NULL value > return > by PyImport_Import() > > following is the code. code is copied from > http://www.codeproject.com/cpp/embedpython_1.asp > > following file is saved as > > call_function.c > > > /************************************************************************************************************/ > > // call_function.c - A sample of calling > // python functions from C code > // > #include <Python.h> > > int main(int argc, char *argv[]) > { > PyObject *pName, *pModule, *pDict, *pFunc, *pValue; > > if (argc < 3) > { > printf("Usage: exe_name python_source function_name\n"); > return 1; > } > > // Initialize the Python Interpreter > Py_Initialize(); > > // Build the name object > pName = PyString_FromString(argv[1]); > > // Load the module object > pModule = PyImport_Import(pName); > > // pDict is a borrowed reference > pDict = PyModule_GetDict(pModule); > > // pFunc is also a borrowed reference > pFunc = PyDict_GetItemString(pDict, argv[2]); > > if (PyCallable_Check(pFunc)) > { > PyObject_CallObject(pFunc, NULL); > } else > { > PyErr_Print(); > } > > // Clean up > Py_DECREF(pModule); > Py_DECREF(pName); > > // Finish the Python Interpreter > Py_Finalize(); > > return 0; > } > > > /************************************************************************************************************/ > python file saved as > > py_function.py > > > /************************************************************************************************************/ > > '''py_function.py - Python source designed to ''' > '''demonstrate the use of python embedding''' > > def multiply(): > c = 12345*6789 > print 'The result of 12345 x 6789 :', c > > > return c > > > /************************************************************************************************************/ > > $gcc -g call_function.c -lpython2.5 -ocall_function > $./call_function py_function.py multiply > > i get following output > > ImportError: No module named py_function > Failed to load "py_function" > > when i kdbg(debug) it i vet NULL value returned from PyImport_Import().. > > can any one please find out the error that i am doing. > > -- > Shrikant >

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Re: [C++-sig] C++-sig Digest, Vol 51, Issue 25
by Shrikant Chikhalkar Oct. 25, 2007

Oct. 25, 2007

Hi, thanks for the reply. that i have already tried. Still i am getting same error. could you please give some pointer that where i am doing wrong. thanks Shrikant On 10/25/07, c++-sig-request(a)python.org <c++-sig-request(a)python.org> wrote: > > Send C++-sig mailing list submissions to > c++-sig(a)python.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.python.org/mailman/listinfo/c++-sig > or, via email, send a message with subject or body 'help' to > c++-sig-request(a)python.org > > You can reach the person managing the list at > c++-sig-owner(a)python.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of C++-sig digest..." > > > Today's Topics: > > 1. failed in PyImport_Import() (Shrikant Chikhalkar) > 2. Re: failed in PyImport_Import() (Gustavo Carneiro) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 25 Oct 2007 12:22:24 +0530 > From: "Shrikant Chikhalkar" <shrikantvc(a)gmail.com> > Subject: [C++-sig] failed in PyImport_Import() > To: c++-sig(a)python.org > Message-ID: > <87de5f460710242352w5b57dc4djbcfba96ccf0f3578(a)mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Hi, > > i am tring to call python function from 'C' program. i get NULL value > return > by PyImport_Import() > > following is the code. code is copied from > http://www.codeproject.com/cpp/embedpython_1.asp > > following file is saved as > > call_function.c > > > /************************************************************************************************************/ > > // call_function.c - A sample of calling > // python functions from C code > // > #include <Python.h> > > int main(int argc, char *argv[]) > { > PyObject *pName, *pModule, *pDict, *pFunc, *pValue; > > if (argc < 3) > { > printf("Usage: exe_name python_source function_name\n"); > return 1; > } > > // Initialize the Python Interpreter > Py_Initialize(); > > // Build the name object > pName = PyString_FromString(argv[1]); > > // Load the module object > pModule = PyImport_Import(pName); > > // pDict is a borrowed reference > pDict = PyModule_GetDict(pModule); > > // pFunc is also a borrowed reference > pFunc = PyDict_GetItemString(pDict, argv[2]); > > if (PyCallable_Check(pFunc)) > { > PyObject_CallObject(pFunc, NULL); > } else > { > PyErr_Print(); > } > > // Clean up > Py_DECREF(pModule); > Py_DECREF(pName); > > // Finish the Python Interpreter > Py_Finalize(); > > return 0; > } > > > /************************************************************************************************************/ > python file saved as > > py_function.py > > > /************************************************************************************************************/ > > '''py_function.py - Python source designed to ''' > '''demonstrate the use of python embedding''' > > def multiply(): > c = 12345*6789 > print 'The result of 12345 x 6789 :', c > > > return c > > > /************************************************************************************************************/ > > $gcc -g call_function.c -lpython2.5 -ocall_function > $./call_function py_function.py multiply > > i get following output > > ImportError: No module named py_function > Failed to load "py_function" > > when i kdbg(debug) it i vet NULL value returned from PyImport_Import().. > > can any one please find out the error that i am doing. > > -- > Shrikant >

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datastructure to numpy and back
by Georg Holzmann Oct. 22, 2007

Oct. 22, 2007

Hallo! I know this was discussed quite some times, but I did find that many workarounds and not really a common way how to do that with Boost.Python ... so I am a little bit confused ... My problem: I have a class with some (big) custom C++ matrix types and I want to write some getters/setters for them to/from numpy arrays, where I want to avoid copies of the data. So is there a common way to do this ? (e.g. num_util from http://www.eos.ubc.ca/research/clouds/software/pythonlibs/num_util/num_util… ?) Or can maybe someone link me to some docu or examples which already did this ? (it must be quite common ...) Many thanks for any hint, LG Georg

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a question about boost python
by Chang Chen Oct. 22, 2007

Oct. 22, 2007

I know we need define a wrapper, but our function signature is quite regular. i.e. only the last parameter is output parameter, so I want to write a template, so that such wrapper can be easily written. Our function definition looks like: void function1(int t1, float t2, string& t3) ; I want to define a template: template <typename Return, typename T1, typename T2, typename TOUT> struct FunctionConvert< Return (*) ( T1 , T2, TOUT& ) > { typedef functionT Return (*) ( T1 , T2, TOUT& ); static TOUT run(functionT P,const T1& t1, const T2& t2) { TOUT out; P(t1,t2,out); return out; } } But I do not know how to integrate it with boost python :(. - Chang

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I can't get None
by Matthew Scouten Oct. 18, 2007

Oct. 18, 2007

I want to return None from a c++ function. I have googled for how to do this with no good results. How do I get an object with None in c++?

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passing a vector of structs
by Matthew Scouten Oct. 17, 2007

Oct. 17, 2007

I have a vector of 'struct foo' in c++ that needs to be passed to a function python. 'struct foo' is an extremely simple structure containing 3 ints and a trivial ctor. so I create a foo_wrapper: struct foo_wrapper : foo , wrapper<foo> { foo_wrapper(const foo& f); foo_wrapper(); }; and export it: class_<foo_wrapper>("foo") .def(init<>()) .def_readwrite("iE", &foo::iE ) .def_readwrite("bA", &foo::bA) .def_readwrite("bL", &foo::bL) ; next I export a vector of foo_wrappers: class_< std::vector<foo_wrapper> >("VectorOfFoo") .def(vector_indexing_suite< std::vector<foo_wrapper>, true >() ); I pass the vector<foo> to a python function: Traceback (most recent call last): File "C:\redacted", line 23, in <module> pc.RequestExchangeList() TypeError: No to_python (by-value) converter found for C++ type: class std::vector<struct foo ,class std::allocator<struct foo > > I try to copy the elements to a new vector<foo_wrapper>, it seems to work fine, untill I try to access an element of that vector and get: Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 7, in OnExchangeList TypeError: No to_python (by-value) converter found for C++ type: struct TTExchangeStruct_wrapper So what am I doing wrong? How am I supposed to pass a vector of structs from c++ to python?

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Re: [C++-sig] Header error in boost/python/object/make_holder?
by David Abrahams Oct. 16, 2007

Oct. 16, 2007

on Wed Oct 10 2007, "Michel Valstar" <Michel.Valstar-AT-imperial.ac.uk> wrote: > I am trying to build code of a recently graduated student, who is now unavailable to us (read: > ignores us). When running scons in the appropriate directory, a lot gets build, until I get the > following error: > > /usr/include/boost/python/object/make_holder.hpp:81: error: 'allocate' is not a member of > 'boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits > <char>, std::allocator<char> >, State> >' > /usr/include/boost/python/object/make_holder.hpp:83: error: no matching function for call to > 'boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits > <char>, std::allocator<char> >, State> >::value_holder(int*&)' > /usr/include/boost/python/object/value_holder.hpp:44: note: candidates are: > boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits > <char>, std::allocator<char> >, State> >::value_holder() > /usr/include/boost/python/object/value_holder.hpp:44: note: > boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits > <char>, std::allocator<char> >, State> >::value_holder(const > boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits > <char>, std::allocator<char> >, State> >&) > scons: *** [trackerbase/trackerbasewrapper.os] Error 1 > scons: building terminated because of errors. > > This does not seem to be an error in his own code, rather an error in the boost.python code? > This is the first time I am using boost, and, as usual, I need to get this program working > yesterday. > > My machine is a recently installed Ubuntu Feisty (hence the need for re-compilation). I am using > the latest version of Boost (boost_1_34_1) and python 2.5.1 > > Any help would be appreciated. I'll try. First, please read the Note at http://boost.org/libs/python/doc/building.html#no-install-quickstart Also, please note that http://boost.org/more/mailing_lists.htm#cplussig may be a better place to ask this question. I'm following up there. I'm pretty sure this is an error in your student's code and the compiler is giving you a poor error message. Most probably std::pair<std::basic_string<char, std::char_traits<char>,std::allocator<char> >, State> is an incomplete type at the point where make_holder is being used. However, guessing is really futile. If my guess is wrong, please prepare and post a minimal, complete example as described in http://article.gmane.org/gmane.comp.python.c++/10237/match=minimal+complete… 9 times out of 10, preparing a minimal example reveals the actual problem to the person asking the question ;-) Cheers, -- Dave Abrahams Boost Consulting http://www.boost-consulting.com

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Problems passing objects to function by const reference
by Patrick Hartling Oct. 16, 2007

Oct. 16, 2007

In our uses of Boost.Python, we have run into a case where very simple code fails to compile. The case that we have is that a class type has no public destructor and instantiations of that type are passed by const reference into a function. The Boost.Python code for exposing the function that accepts the objects fail to compile because an attempt is made to call the non-public destructor. The attached code demonstrates what we are trying to do. The compile error from GCC 4.1 when compiling against Boost 1.34.1 is as follows: destroy_test.h: In static member function 'static void boost::python::detail::value_destroyer<false>::execute(const volatile T*) [with T = C]': .../boost-1.34.1/include/boost-1_34_1/boost/python/detail/destroy.hpp:90: instantiated from 'void boost::python::detail::destroy_referent_impl(void*, T& (*)()) [with T = const C]' .../boost-1.34.1/include/boost-1_34_1/boost/python/detail/destroy.hpp:101: instantiated from 'void boost::python::detail::destroy_referent(void*, T (*)()) [with T = const C&]' .../boost-1.34.1/include/boost-1_34_1/boost/python/converter/rvalue_from_python_data.hpp:135: instantiated from 'boost::python::converter::rvalue_from_python_data<T>::~rvalue_from_python_data() [with T = const C&]' .../boost-1.34.1/include/boost-1_34_1/boost/python/converter/arg_from_python.hpp:108: instantiated from 'PyObject* boost::python::detail::caller_arity<1u>::impl<F, Policies, Sig>::operator()(PyObject*, PyObject*) [with F = void (*)(const C&), Policies = boost::python::default_call_policies, Sig = boost::mpl::vector2<void, const C&>]' .../boost-1.34.1/include/boost-1_34_1/boost/python/object/py_function.hpp:38: instantiated from 'PyObject* boost::python::objects::caller_py_function_impl<Caller>::operator()(PyObject*, PyObject*) [with Caller = boost::python::detail::caller<void (*)(const C&), boost::python::default_call_policies, boost::mpl::vector2<void, const C&> >]' generated.cpp:21: instantiated from here destroy_test.h:4: error: 'C::~C()' is protected .../boost-1.34.1/include/boost-1_34_1/boost/python/detail/destroy.hpp:33: error: within this context I have tried to understand what Boost.Python is doing internally, and it seems like a copy of the object is being made that is later cleaned up by calling the destructor explicitly. I could definitely be wrong about that assessment, though. Ultimately, what I don't understand is why anything needs to be destroyed in this case. -Patirck -- Patrick L. Hartling http://www.137.org/patrick/

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a question about boost python
by Chang Chen Oct. 16, 2007

Oct. 16, 2007

Hi All I have a set of functions which last parameters are out-parameter. i.e. void function1(int t1, float t2, string& t3) ; I want to expose these functions in python, but such definition (~def("function1", function1)~) is not what I want. Because we have to write python code like this: strTest='' function1(1,2.0,strTest); I prefer to writing python code like this strTest = funciton1(1,2.0) Is there any idea to solve this question? Thanks

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