Mailman 3 December 2003 - Cplusplus-sig

RE: [C++-sig] Re: Wrapper for exception translation
by Gottfried.Ganssauge＠HAUFE.DE Dec. 13, 2004

Dec. 13, 2004

> > ... > >> > >> > Currently, in order to wrap user defined exceptions you need to > >> > > >> > - allocate a python exception using PyErr_NewException > >> > >> Well, no. I don't see any call to PyErr_NewException in > >> libs/python/test/exception_translator.cpp > > > > Right, you don't need to if you are content with RuntimeError > > exceptions. > > or any other pre-packaged exception type provided by Python. > > > My objective was another one: I wanted to create module exceptions > > that are derived from the python "Exception" class. > >> > >> > This function needs to be parametrized using a specific naming > >> > convention > >> > >> It's not clear to me what you're referring to. Are you > sure you mean > >> "naming convention"? > > Yes. > > From the documentation to PyErr_NewException: > > > > ... The __module__ attribute of the new class is set to > the first part > > (up to the last dot) of the name argument, and the > class name is set to > > the last part (after the last dot). > > ...yeah, that's a naming convention, but I don't see how that affects > the parameterization of any function. It is enforced by PyErr_NewException, so you must follow this convention. On the hand I don't think that any user of boost.python is aware of that convention, so I wanted to codify it within my facility. ... > > What I wanted to achieve was the following: > > Create an instance of a translated_exception_handler<> t > which will be > > registered with the library by calling > > register_exception_translator<>(). > > Sorry to be difficult, but I'm going to contradict you. You didn't > want any of that. What you wanted was to create a new Python > exception type in the module which would correspond to a particular > C++ exception type and would be raised at the boundary with Python > whenever a wrapped function threw the C++ exception. Right? Right. I actually described the way to do it within the current library design. > > > Normally t would be destructed by the end of exception_<>() thereby > > leaving a registration to a non-existing translator - very bad > > karma. > > I don't understand any of this. All you have to pass to > register_exception_translator is a function pointer, and functions > live forever. So where's the lifetime issue? A pointer to a function which has access to python exception instance e. As I didn't want to create separate entities I chose to supply a functor instead which has e as a member variable. > > > Because I didn't like to have an additional container for all > > translated_exception_handler<> instances, I chose to store t within > > e's class dictionary. At that moment it seemed to be the easiest > > way to create a wrapper class using class_<> instead of making a > > true python class by hand (and it even works!). You are right, it > > is way too complex, I will change it to the mechanism I used in > > opaque_pointer_converter. > > I don't know what that is, but before you consider doing something > which is again too complex, please consider: > > template <class E> > struct translate_exception > { > static char const* msg; This would need to be defined somewhere. > static object python_exception_type; ... and this would need to be defined somewhere as well. > > static void handler(E const&) > { > PyErr_SetString(python_exception_type.ptr(), msg.c_str()); > }; > > translate_exception(char const* python_exception_name, > char const* msg_) > { > // need fancier name manipulation here > python_exception_type > = object( > handle<>(PyErr_NewException(name))); > msg = msg_; > register_exception_translator<E>(handler); > } > }; > > > Simple. Yes. ... > > I'll make a redesign ... At times you don't see the forrest, just trees ... I think this time I have a simple facility which is also easy to use (no macros). It could be even simpler with a completely different design but frankly - I have no clue how to implement that: We would need a way to somehow derive (in the python sense) a class_<> from PyExc_Exception (the type of the python Exception class) or any other python class (PyErr_NewException() has a base parameter, which could be used for that). At the same time an exception_translator should be registered for that class_<> which uses PyErr_SetObject() to raise a copy of the exception caught. This would allow us to have true Python exceptions in a pythonic sense directly wrapped around the corresponding C++ exception. > > Thnx for your feedback. > > Cool! Looking forward to it. > > -- > Dave Abrahams > Boost Consulting > www.boost-consulting.com Cheers, Gottfried

3 7

Boost Python and Intel C++ 7.1 windows
by Xavier WARIN(Compte LOCAL) - I23 Aug. 16, 2004

Aug. 16, 2004

Hi, While compiling with Intel C++ 7.1 Boost Python , i get this kind of error on class.cpp and a lot of other Boost Python files : C:\boost-1.30.2\boost/type_traits/is_integral.hpp(39): error: class "boost::is_integral<unsigned short>" has already been defined BOOST_TT_AUX_BOOL_TRAIT_CV_SPEC1(is_integral,wchar_t,true) I think that there must be a define that i missed somewhere ! I don't find it Any idea ? Thank you Xavier Warin

2 2

indexing_v2 status update
by Raoul Gough Jan. 25, 2004

Jan. 25, 2004

Here's a status report on the indexing_v2 work I've been doing: o I've improved the handling for containers of shared_ptr's, so that sorting and searching automatically do the right indirection. o Fixed various layout and naming convention issues o container_proxy is now strongly exception safe (commit or rollback) o The container_proxy Generator parameter now works even on MSVC6 o I've added a Flags parameter to allow expensive features (in terms of object code size) to be selectively disabled. o I've added convenience templates for use without partial template specialization support (vector_suite, map_suite, etc.) These last two points bring the interface a little closer to what Joel de Guzman had originally, although the flags that he used were passed separately as individual bool parameters instead of as flag bits. He certainly wasn't kidding about the extra effort in supporting MSVC6. So as far as I know, there is no outstanding coding work remaining for the current level of functionality. I'm now updating the documentation to reflect the recent changes, and then the suite, in my opinion, will be ready for release. One possible extension I've been thinking about, as suggested by Ralf W. Grosse-Kunstleve, is the idea of allowing construction of a container from a Python iterable object: e.g. v = Vector ([1,2,3]) The ideal way to do it would be to massage the single input parameter into two C++ iterators that could be passed to the templated vector constructor, but I haven't looked far enough into the constructor dispatching internals to know how to do this, or even if it is possible. The problem, AFAICS, would be knowing when to select that overload of the constructor and when not to, and how/where to insert the necessary code to create the two iterators from the single Python object. Any advice would be appreciated. This might also be significant for another of Ralf's suggestions - pickling support. So I have two loosely related questions - what do people thing about including the current indexing_v2 suite in release 1.31, and should I try adding the iterator-based constructor support? -- Raoul Gough. export LESS='-X'

7 48

class_<>::add_property() on CVS-HEAD
by Jonathan Brandmeyer Jan. 3, 2004

Jan. 3, 2004

The following example demonstrates a method of using add_property that works with Boost.Python 1.30 but not CVS-HEAD (from sourceforge CVS). The example posted is somewhat useless as-is, but demonstrates something that I started using for properties with non-trivial accessors. Is there a replacement for this functionality? Thanks, Jonathan Brandmeyer -------------------------------------------------------------- #include <boost/python.hpp> namespace test { // Hmm. return_internal_reference<>() wants to wrap a real class. class ret_type { public: double i; }; class crash_me { private: ret_type i; public: ret_type& get_i() { return i; } }; } BOOST_PYTHON_MODULE( crash_test) { using namespace boost::python; class_< test::ret_type>( "ret_type") .def_readwrite( "i", &test::ret_type::i) ; class_< test::crash_me> crash_me_wrapper( "crash_me"); crash_me_wrapper .def( "get_i", &test::crash_me::get_i , return_internal_reference<>()) ; // The following works under Boost 1.30, but not CVS-HEAD // (sourceforge repository). crash_me_wrapper.add_property( "i", crash_me_wrapper.attr("get_i")); } -------------------------------------------------------- Testing with G++ 3.3.2 (Debian) results in the following error using CVS-HEAD: /home/jonathan/src/boost-CVS-HEAD/boost/boost/python/class.hpp: In member function `boost::python::api::object boost::python::class_<T, X1, X2, X3>::make_fn(const F&) [with F = boost::python::api::proxy<boost::python::api::attribute_policies>, T = test::crash_me, X1 = boost::python::detail::not_specified, X2 = boost::python::detail::not_specified, X3 = boost::python::detail::not_specified]': /home/jonathan/src/boost-CVS-HEAD/boost/boost/python/class.hpp:365: instantiated from `boost::python::class_<T, X1, X2, X3>& boost::python::class_<T, X1, X2, X3>::add_property(const char*, Get) [with Get = boost::python::api::proxy<boost::python::api::attribute_policies>, T = test::crash_me, X1 = boost::python::detail::not_specified, X2 = boost::python::detail::not_specified, X3 = boost::python::detail::not_specified]' crashme.cpp:38: instantiated from here /home/jonathan/src/boost-CVS-HEAD/boost/boost/python/class.hpp:429: error: no matching function for call to `get_signature(const boost::python::api::proxy<boost::python::api::attribute_policies>&, test::crash_me*)'

2 3

Sharing Singleton instances across boost.python extension modules
by Joel Gerard Jan. 2, 2004

Jan. 2, 2004

Hi all, How do I share singleton instances across extension modules in Windows? For instance, if I have an instance of a memory manager in one DLL, how do I use the same memory manager in the other? I realise this is a big question, but any links, references etc would be appreciated. Is it even possible? Joel ===== __________________________________ Do you Yahoo!? The New Yahoo! Shopping - with improved product search http://shopping.yahoo.com

2 1

args.hpp from CVS
by Nikolay Mladenov Dec. 31, 2003

Dec. 31, 2003

There is a problem in the args.hpp from the CVS(today) I am getting this error H:\work\include\ui/selection.h(145) : warning C4355: 'this' : used in base member initializer list D:\Shared\boost_1_31_0\boost\boost/python/args.hpp(145) : error C2039: ',' : is not a member of 'keywords<1>' D:\Shared\boost_1_31_0\boost\boost/python/args.hpp(58) : see declaration of 'keywords<1>' H:\work\src\ui\angle_field_py.cpp(130) : see reference to function template instantiation 'struct boost::python::detail::keywords<2> __cdecl boost::python::detail::operator ,(const struct boost::python::detail::keywords<1> &, char *)' being compiled This fixes it: $ cvs diff args.hpp Index: args.hpp =================================================================== RCS file: /boost/boost/boost/python/args.hpp,v retrieving revision 1.18 diff -r1.18 args.hpp 145c145 < return l.operator,(arg(name)); --- > return l,arg(name); -- Nikolay Mladenov Sitius Automation Inc. www.sitius.com

3 5

error accessing attribute
by Stefan Seefeld Dec. 31, 2003

Dec. 31, 2003

hi there, I'm compiling a python frontend for some classes, exposing a member variable (pointer to object) as a property in python. Unfortunately, when I access that property, I get the error: TypeError: bad argument type for built-in operation What can cause this kind of error ? What built-in operation is meant here ? And what would be the argument ? I'm sorry that I can't provide a more detailed description of the problem, unfortunately I could not yet reproduce the problem with a simple test case. Is there any documentation (FAQ, wiki, whatever) that discusses often encountered error messages (which can get quite cryptic with the combination of python runtime binding and C++ template compile-time binding !) and their respective meaning / typical cause ? Thanks a lot, Stefan

3 4

IntWrapper.hpp in indexing_suite
by Niall Douglas Dec. 31, 2003

Dec. 31, 2003

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Firstly, let me confirm I have this right: IntWrapper is converted into an int by bpl using the operator boost::shared_ptr<IntWrapper>() const yes? Or is it the implicitly_convertible? If it is the latter, why do we need the shared_ptr<> operator? Anyway I came up with the below by basically following the testlinear.cpp example but unfortunately it complains "TypeError: No to_python (by-value) converter found for C++ type: class boost::python::indexing::iterator_pair<class CArrayMember<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > *>". The code I used was: >>> from TestCArrays import * >>> a=MyList() >>> b=a.getData() I don't get why it's failing to find the conversion with mine whereas it works with the test :( Any help much appreciated. Cheers, Niall - --- cut --- #include <boost/python.hpp> #include <boost/python/suite/indexing/container_suite.hpp> #include <boost/python/suite/indexing/iterator_pair.hpp> #include <boost/python/suite/indexing/container_proxy.hpp> #include <string> class MyList { std::string *array; public: MyList(); std::string *getData() { return array; } }; MyList::MyList() { static std::string data[]={ std::string("Niall"), std::string("is"), std::string("a"), std::string("teapot") }; arrayÚta; } template<class T> class CArrayMember : public T { public: CArrayMember() : T() { } CArrayMember(const CArrayMember &o) : T(o) { } explicit CArrayMember(const T &o) : T(o) { } operator boost::shared_ptr<CArrayMember>() const { return boost::shared_ptr<CArrayMember>(new CArrayMember(*this)); } }; typedef boost::python::indexing::iterator_pair<CArrayMember<std::string> *> MyListCArray; MyListCArray MyList_getArray(MyList &l) { CArrayMember<std::string> *data=static_cast<CArrayMember<std::string> *>(l.getData()); return boost::python::indexing::iterator_pair<CArrayMember<std::string> *> (data, data+100000); // Issue if l is near the 4Gb mark } BOOST_PYTHON_MODULE(TestCArrays) { boost::python::implicitly_convertible<std::string, CArrayMember<std::string> >(); boost::python::class_< MyListCArray, boost::noncopyable>("MyListCArray", boost::python::init<CArrayMember<std::string> *, CArrayMember<std::string> *>()) .def(boost::python::indexing::container_suite< MyListCArray >()); boost::python::class_< MyList, boost::noncopyable >("MyList") .def("getData", &MyList_getArray) ; } -----BEGIN PGP SIGNATURE----- Version: idw's PGP-Frontend 4.9.6.1 / 9-2003 + PGP 8.0.2 iQA/AwUBP4d9/8EcvDLFGKbPEQLYxwCfSIKfJ6mtqNtS76pbNYxTF4OvZZUAoL+3 4O1w8HK0sgRIaFPbxZ5WXbfV =d8TG -----END PGP SIGNATURE-----

5 22

register_ptr_to_python and get_pointer
by Marc Kwiatkowski Dec. 28, 2003

Dec. 28, 2003

I'm trying to integrate Boost::python templates to expose a bunch of legacy classes. We have our own reference-counting pointer template, ref_ptr; the moral equivalent of shared_count. Having gotten basic classes, I set out to figure out how to to expose ref_ptr. Looking at the notes on this list and the PythonInfoWiki I figured out how to wrap my classes with shared_ptr using register_ptr_to_python. I then attempted to switch from shared_ptr to our own ref_ptr and kept getting cryptic errors like the following: boost\python\object\make_ptr_instance.hpp(31) : error C2784: 'T *boost::python::get_pointer(const boost::python::handle<T> &)' : could not deduce template argument for 'const boost::python::handle<T> &' from 'const ref_ptr<TRef>' I am not a C++ template god by any stretch of the imagination, but I was determined to try to make this work or at least understand why it wouldn't. After dissecting pointee, pointer_holder, make_instance, et al., I finally realized that my problem was that there was no get_pointer template function for class instances of my ref_ptr template. All I needed to do was the following: namespace boost { namespace python { /* Need to provide get_pointer template function for SigFoundation::ref_ptr, so that boost holder templates can use it to extract values. */ template <class T> T* get_pointer(example::ref_ptr<T> const& p) { return p.get(); } }} // namespace boost::python With this in place, I was able to get my version of the register_ptr_to_python sample working. (It's included below in toto for your reference.) I guess the question I have ism why isn't this documented anywhere? I have found boost::python to be the best library for getting at C++ stuff from python, but the terseness of the documentation and lack of examples for integrating with legacy code is frustrating. Also, if this isn't the correct way to do this, I'd be glad to know what is. Here is the register_python_to_pointer sample modified for a thirdparty ref-counting-pointer template: Thanks. === test.cpp === #include <xstring> #include <boost/python/class.hpp> #include <boost/python/module.hpp> #include <boost/python/def.hpp> #include <boost/python/call_method.hpp> #include <boost/python/register_ptr_to_python.hpp> #include <boost/python/exception_translator.hpp> #include <boost/python/overloads.hpp> #include <boost/python/pointee.hpp> #include <boost/python/converter/arg_from_python.hpp> namespace boost { namespace python { /* Need to provide get_pointer template function for example::ref_ptr, so that boost holder templates can use it to extract values. */ template <class T> T* get_pointer(example::ref_ptr<T> const& p) { return p.get(); } }} // namespace boost::python namespace example { namespace test { namespace ref_ptr { using boost::shared_ptr; using boost::is_pointer; using boost::remove_pointer; using boost::python::call_method; using boost::python::class_; using boost::python::def; using boost::python::init; using boost::python::pointee; using boost::python::register_exception_translator; using boost::python::register_ptr_to_python; using boost::python::to_python_converter; using std::wstring; class C { public: C() : str(L"hello ref_ptr") {} C(wstring const& aString) : str(aString) {} virtual ~C() {} virtual wstring GetString() const { return str; } private: wstring str; }; class Factory { public: Factory() {} CVxRefPtr< C > NewC(wstring const& aString) { return CVxRefPtr< C >(new C(aString)); } wstring frpc(CVxRefPtr< C > c) {return c->GetString();} wstring fconstc(C const& c) { return c.GetString();} wstring fc(C& c) { return c.GetString();} }; class C_Wrapper: public C { public: C_Wrapper(PyObject* self_) : C(), self(self_) {} C_Wrapper(PyObject* self_, wstring const& aString) : C(aString), self(self_) {} C_Wrapper(PyObject* self_, const C& c): self(self_), C(c) {} ~C_Wrapper() {} wstring GetString() const { return call_method<wstring>(self, "GetString"); } wstring default_GetString() const { return C::GetString(); } PyObject* self; }; BOOST_PYTHON_MODULE(test) { class_<C, C_Wrapper >("C") .def(init<wstring const&>()) .def("GetString", &C::GetString, &C_Wrapper::default_GetString); register_ptr_to_python< CVxRefPtr< C > >(); class_<Factory>("Factory") .def("NewC", &Factory::NewC) .def("frpc", &Factory::frpc) .def("fconstc", &Factory::fconstc) .def("fc", &Factory::fc); } }}} // namespace example::test::ref_ptr === test.py === from test import C, Factory f=Factory() x=f.NewC("fba") c=C("foo") f.frpc(x) # succeeds f.frpc(c) # fails f.fc(x) # succeeds f.fc(c) # succeeds f.fconstc(x) # succeeds f.fconstc(c) # succeeds -- marc.kwiatkowski(a)veritas.com

3 11

boost: python may cause memory leaks?
by Leo Yee Dec. 27, 2003

Dec. 27, 2003

Hi, friends, I use VS 7.1 and I have following code: #include "stdafx.h" #include <crtdbg.h> using namespace boost::python; class cPart { public: void set_text( const std::string &t ) { _text = t; } std::string text( void ) { return _text; } private: std::string _text; }; BOOST_PYTHON_MODULE(hello) { class_<cPart, boost::noncopyable >("cPart") .add_property( "text", cPart::text, cPart::set_text ); } int _tmain(int argc, _TCHAR* argv[]) { _CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF ); if (PyImport_AppendInittab("hello", inithello) == -1) return 1; Py_Initialize(); PyRun_SimpleString( "from hello import *\n" "p = cPart()\n" "p.text = 'hello'\n" "print p.text\n" ); Py_Finalize(); getchar(); return 0; } I compiled the code and ran it. Everything was ok except I got memory leaks from the output window of the VS like these: Detected memory leaks! Dumping objects -> {54} normal block at 0x003E5AD8, 8 bytes long. Data: < RE A > 10 52 45 00 83 BE 41 00 {53} normal block at 0x003E5A90, 8 bytes long. Data: <(RE A > 28 52 45 00 D6 B6 41 00 {52} normal block at 0x003E5A48, 8 bytes long. Data: <lRE l A > 6C 52 45 00 6C B2 41 00 Object dump complete. I just wonder if I really got memory leaks or it was just a illusion. Any suggestion would be appreciated. Leo Yee

4 8