Mailman 3 January 2006 - Cplusplus-sig

C++ singleton
by Emmanuel Taurel Oct. 31, 2007

Oct. 31, 2007

Hello everybody, I am actually writing an interface to python for an existing C++ library using Boost. This library has a C++ singleton class. This class has only one constructor (with arguments) which is "protected" because it's a singleton. I am not able to build a Boost interface to this class because the compiler complains that the constructor I have given to Boost in the class_xxx constructor argument is not public (which is true) ! Therefore, my question is simple : How is it possible to interface such a class with only one constructor which is protected and a static method to create/access the object ? Thank's very much for your answer. Sincerely Emmanuel Taurel (etaurel(a)cells.es) PS : By the way, is there a searchable archive of this mailing list ?

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optimizing away calls to the python runtime -- was [detecting if a function is written in python or C++]
by Mathieu Lacage May 15, 2006

May 15, 2006

hi, I apologize for this second email but the more I think about what I am trying to do, the less I see how to do it. So, here is a hopefully detailed explanation of what I am trying to achieve. Here are my c++ classes: class Event { virtual void notify (void) = 0; }; class Simulator { void schedule (Event *event); double now_s (void); // return current time. void run (void); }; sample c++ use code: class MyEvent : public Event { virtual void notify (void) { std::cout << "now=" Simulator::now_s () << std::endl; delete this; } }; Simulator->schedule (new MyEvent ()); Simulator->run (); // invokes MyEvent::notify sometime later. This sort of code requires a lot of "forwarding code". That is, you often have to write a bunch of Event-deriving classes whose sole purpose in life is to forward the call to their notify method to a call to another class' method with event-specific parameters. So, I have a small make_event c++ template which can be used to do this sort of thing: class MyClass { void random_stuff (double id) { std::cout << "id="<<id<<"now=" Simulator::now_s () << std::endl; } }; MyClass *obj = new MyClass (); Simulator->schedule (make_event (&MyClass::random_stuff, obj, 10.0)); Simulator->run (); Okay, so, to wrap this, I wrapped my Simulator class and my EventWrap class: struct EventWrap : yans::Event { EventWrap( PyObject* self_); virtual ~EventWrap(); virtual void notify (void); private: PyObject *m_self; }; EventWrap::EventWrap (PyObject* self_) : m_self(self_) { Py_INCREF(m_self); } EventWrap::~EventWrap() { Py_DECREF(m_self); } void EventWrap::notify (void) { call_method<void>(m_self, "notify"); delete this; } namespace boost { namespace python { template <> struct has_back_reference<EventWrap> : mpl::true_ {}; }} void export_event (void) { class_<EventWrap, std::auto_ptr<EventWrap>, boost::noncopyable> event ("Event"); event.def ("notify", pure_virtual(&Event::notify)); } void simu_insert_in_s (double delta, std::auto_ptr<EventWrap> ev) { Simulator::insert_in_s (delta, ev.get ()); ev.release (); } void export_simulator (void) { def ("run", Simulator::run); def ("insert_in_s", simu_insert_in_s); } which allows me to write the following python code: class __MyEvent__(Event): def set_callback (self, function, *args): self.__function_ = function; self.__args_ = args; def notify (self): self.__function_ (*self.__args_); def make_event(function, *args): ev = __MyEvent__ (); ev.set_callback (function, *args); return ev def my_nothing0 (): print "my model now=%f" % simulator.now_s (); simulator.insert_in_s (4.0, make_event (my_nothing1, 99)); simulator.run () okay, so all of this stuff works really nicely but there is a catch. I would like to be able to write code such as: simulator.insert_in_s (4.0, make_event (simulator.now_s)); simulator.run () and ensure that once simulator.run has reached the Simulator::run c++ method, no python code will be executed ever. Namely, I want call to make_event to generate a nice C++ Event class which will not call back into python's __MyEvent__.notify before calling simulator.now_s and Simulator::now_s. i.e., it should call back Simulator::now_s directly. The more I think about this, the less I see a way to do this with boost. Have I missed something ? Mathieu --

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GCC version compatibility
by David Abrahams April 15, 2006

April 15, 2006

The following message is a courtesy copy of an article that has been posted to gmane.comp.python.devel as well. Recently people testing Boost.Python with GCC on Linux have reported that the extensions being tested have to be compiled with exactly the same version of GCC as the Python they're being loaded into, or they get mysterious crashes. That doesn't correspond to my past experience; it has always been true that, as long as the compiler used to build Python and the one used to build the extension have compatible 'C' ABIs, we've been okay. Yes, if you were going to pass types like FILE* across the Python/C API, then you additionally need to be sure that the two compilers are using the same 'C' library. That said, none of the Boost.Python tests do that. I'm wondering if there has been a well-known recent change either in Python or GCC that would account for these new reports. Any relevant information would be appreciated. -- Dave Abrahams Boost Consulting www.boost-consulting.com

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RE: Wrapper for exception translation
by Gottfried.Ganssauge＠HAUFE.DE April 4, 2006

April 4, 2006

> -----Original Message----- > From: David Abrahams [mailto:dave@boost-consulting.com] > Sent: Monday, December 13, 2004 1:04 PM > To: c++-sig(a)python.org; Gottfried Ganßauge > Subject: Re: Wrapper for exception translation > > > Gottfried Ganßauge wrote: > > Hi Dave, > > > > I digged through the class_<> implementation and I think I > know what I > > must do to implement it. Like you suggested I would add another > > argument to the class_base constructor which is used as > another base > > class for the newly created class. > > Hi Gottfried, Hi Dave, > > I don't know if you're still listening, but today I offered to > implement this patch on the C++-sig (see my other post). > Are you still interested? I am still listening but was buried deeply with work so I even had to abandon the work already invested into this. Nonetheless: Yes - I'm still interested. Cheers, Gottfried P.S.: What second Post? I got 2 Copies of this one. > > > > -- > Dave Abrahams > Boost Consulting > http://www.boost-consulting.com >

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Trying to clone (again)
by Paul F. Kunz Feb. 24, 2006

Feb. 24, 2006

I'm trying to clone a Python object from C++. The Python class inherits from an exposed C++ base class. To avoid the dangling pointer problem, I keep a Python reference to the created Python object like this... from hippo import FunctionBase # Define a class in Python that is derived from C++ base class _clones = [] class Linear ( FunctionBase ) : def __init__ ( self ) : FunctionBase.__init__( self ) self.initialize () def clone ( self ) : _clones.append ( Linear () ) return _clones[-1] Then in the C++ wrapper class, I have FunctionBase * FunctionWrap:: clone () const // overrides FunctionBase::clone() { #ifndef HAVE_OLD_PYTHON PyGILState_STATE state = PyGILState_Ensure (); object py_result; if (override clone = this->get_override("clone")) { try { // The Python class author overrode clone; do // whatever she says py_result = clone(); } catch ( error_already_set & e ) { PyErr_Print (); handle_exception (); PyGILState_Release ( state ); return 0; } } else { The Python implemented clone() member function is called but I get the following error message on return ... TypeError: No registered converter was able to extract a C++ reference to type boost::python::api::object from this Python object of type Linear Any suggestions?

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easy method for converting boost::tuple to python tuple?
by Grant Goodyear Feb. 17, 2006

Feb. 17, 2006

I have a c++ function that returns boost::tuple<double, float, int>. From python I get the following when I try to access this function:: No to_python (by-value) converter found for C++ type: boost::tuples::tuple<double, float, int, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> Fair enough, I need to tell boost.python what to do. Google provides the following link: http://mail.python.org/pipermail/c++-sig/2002-July/001722.html which is a tad dated. Is there a simple way to tell boost.python how to perform the conversion? Thanks, Grant Goodyear -- Grant Goodyear web: http://www.grantgoodyear.org e-mail: grant(a)grantgoodyear.org

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pyplusplus tutorials & GUI wizard
by Roman Yakovenko Feb. 13, 2006

Feb. 13, 2006

Hi. pyplusplus project made first step towards ( better ) documentation. I created step by step tutorials. You can find it here: http://language-binding.net/pyplusplus/tutorials.html Also pyplusplus GUI has wizard. It will generate pyplusplus code for you. In order to try it you need cvs version. What is pyplusplus? pyplusplus is an object-oriented framework for creating a code generator for boost.python library All comments, suggestions or correction are welcome. Enjoy Roman Yakovenko

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Pyplusplus templates and roadmap
by Allen Bierbaum Feb. 13, 2006

Feb. 13, 2006

I am looking at using pyplusplus to replace my current usage of Pyste on one of my projects. In reading through the comparison between the two (http://www.language-binding.net/pyplusplus/to_pyste_comparison.html) it looks like pyplusplus does not support templates. Unfortunately my current project makes extensive use of templates so I may need to hold off on converting it. Taking that in account, is there a development roadmap for future features of pyplusplus? Will it support templates at any point in the near future. Thanks, Allen

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Patch implementing void * support
by Niall Douglas Feb. 12, 2006

Feb. 12, 2006

The enclosed patch adds void * support to Boost.Python by making void an opaque type. Code that uses void * "just works" with this patch with no further effort required. Also enclosed is a testcase and the docs have been modified. Ran full testsuite on msvc7.1 and msvc6 - everything works. I don't have GCC to hand ATM, but apart from maybe a missing typename specifier I can't see anything which would fault. Cheers, Niall Only in boost: bin diff -aur boost_1_33_0/boost/python/converter/registered.hpp boost/boost/python/converter/registered.hpp --- boost_1_33_0/boost/python/converter/registered.hpp 2005-05-18 02:34:36.000000000 +0100 +++ boost/boost/python/converter/registered.hpp 2005-11-06 15:18:14.000000000 +0000 @@ -77,15 +77,35 @@ } template <class T> - registration const& - registry_lookup(T&(*)()) + inline registration const& + registry_lookup2(T&(*)()) { detail::register_shared_ptr1((T*)0); return registry::lookup(type_id<T&>()); } template <class T> - registration const& registered_base<T>::converters = detail::registry_lookup((T(*)())0); + inline registration const& + registry_lookup1() + { + return registry_lookup2((T(*)())0); + } + + template <> + inline registration const& +#ifdef BOOST_NO_CV_VOID_SPECIALIZATIONS + registry_lookup1<void>() +#else + registry_lookup1<const volatile void>() +#endif + { + detail::register_shared_ptr1((void*)0); + return registry::lookup(type_id<void>()); + } + + template <class T> + registration const& registered_base<T>::converters = detail::registry_lookup1<T>(); + } }}} // namespace boost::python::converter diff -aur boost_1_33_0/boost/python/lvalue_from_pytype.hpp boost/boost/python/lvalue_from_pytype.hpp --- boost_1_33_0/boost/python/lvalue_from_pytype.hpp 2004-08-20 12:09:16.000000000 +0100 +++ boost/boost/python/lvalue_from_pytype.hpp 2005-11-06 16:53:14.000000000 +0000 @@ -15,12 +15,25 @@ namespace detail { + struct voidptrholder; // Used to indicate a void * is being extracted + + template <class T> + inline type_info extractor_type_id2() + { + return type_id<T>(); + } + template <> + inline type_info extractor_type_id2<voidptrholder>() + { + return type_id<void>(); + } + // Given a pointer-to-function of 1 parameter returning a reference // type, return the type_id of the function's return type. template <class T, class U> inline type_info extractor_type_id(T&(*)(U)) { - return type_id<T>(); + return extractor_type_id2<T>(); } // A function generator whose static execute() function is an lvalue diff -aur boost_1_33_0/boost/python/opaque_pointer_converter.hpp boost/boost/python/opaque_pointer_converter.hpp --- boost_1_33_0/boost/python/opaque_pointer_converter.hpp 2004-08-20 12:09:16.000000000 +0100 +++ boost/boost/python/opaque_pointer_converter.hpp 2005-11-06 17:16:25.000000000 +0000 @@ -15,6 +15,7 @@ # include <boost/python/detail/none.hpp> # include <boost/type_traits/remove_pointer.hpp> # include <boost/type_traits/is_pointer.hpp> +# include <boost/type_traits/is_void.hpp> // opaque_pointer_converter -- // @@ -54,6 +55,15 @@ , detail::opaque_pointer_converter_requires_a_pointer_type<Pointer> >::type ptr_type; + typedef typename ::boost::remove_pointer<ptr_type>::type noptr_type; + typedef typename mpl::if_c< + ::boost::is_void<typename noptr_type>::value, + detail::voidptrholder, + typename noptr_type + >::type fixed_type; + + typedef typename ::boost::add_reference<typename fixed_type>::type ref_type; + private: struct instance; @@ -84,10 +94,10 @@ return (result); } - static typename ::boost::remove_pointer<ptr_type>::type& + static typename ref_type execute(instance &p_) { - return *p_.x; + return *(typename fixed_type *) p_.x; } private: @@ -132,4 +142,8 @@ } \ }} # endif + +// Declare void as an opaque type for automatic void * usage +BOOST_PYTHON_OPAQUE_SPECIALIZED_TYPE_ID(void) + # endif // OPAQUE_POINTER_CONVERTER_HPP_ Only in boost/libs/python/build/VisualStudio: Debug Only in boost_1_33_0/libs/python/build/VisualStudio: boost_python.dsp Only in boost_1_33_0/libs/python/build/VisualStudio: boost_python.dsw Only in boost/libs/python/build/VisualStudio: boost_python.ncb Only in boost/libs/python/build/VisualStudio: boost_python.sln Only in boost/libs/python/build/VisualStudio: boost_python.suo Only in boost/libs/python/build/VisualStudio: boost_python.vcproj Only in boost/libs/python/build: bin-stage diff -aur boost_1_33_0/libs/python/doc/v2/faq.html boost/libs/python/doc/v2/faq.html --- boost_1_33_0/libs/python/doc/v2/faq.html 2004-11-28 03:54:58.000000000 +0000 +++ boost/libs/python/doc/v2/faq.html 2005-11-06 17:17:31.000000000 +0000 @@ -67,8 +67,6 @@ >error C2064: term does not evaluate to a function taking 2 arguments</a> </dt> - <dt><a href="#voidptr">How do I handle <tt>void *</tt> conversion?</a></dt> - <dt><a href="#custom_string" >How can I automatically convert my custom string type to and from a Python string?</a></dt> @@ -694,29 +692,6 @@ <p>(The bug has been reported to Microsoft.)</p> <hr> - <h2><a name="voidptr"></a>How do I handle <tt>void *</tt> conversion?</h2> - <font size="-1"><i>Niall Douglas provides these notes:</i></font><p> - For several reasons Boost.Python does not support <tt>void *</tt> as - an argument or as a return value. However, it is possible to wrap - functions with <tt>void *</tt> arguments or return values using - thin wrappers and the <i>opaque pointer</i> facility. E.g.: - <pre>// Declare the following in each translation unit -struct void_ {}; -BOOST_PYTHON_OPAQUE_SPECIALIZED_TYPE_ID(void_); - -void *foo(int par1, void *par2); - -void_ *foo_wrapper(int par1, void_ *par2) -{ - return (void_ *) foo(par1, par2); -} -... -BOOST_PYTHON_MODULE(bar) -{ - def("foo", &foo_wrapper); -}</pre> - - <hr> <h2><a name="custom_string"></a>How can I automatically convert my custom string type to and from a Python string?</h2> <font size="-1"><i>Ralf W. Grosse-Kunstleve provides these diff -aur boost_1_33_0/libs/python/test/Jamfile boost/libs/python/test/Jamfile --- boost_1_33_0/libs/python/test/Jamfile 2005-07-07 15:00:30.000000000 +0100 +++ boost/libs/python/test/Jamfile 2005-11-06 15:28:29.000000000 +0000 @@ -151,6 +151,7 @@ [ bpl-test extract ] [ bpl-test opaque ] +[ bpl-test voidptr ] [ bpl-test pickle1 ] [ bpl-test pickle2 ] Only in boost/libs/python/test: bjam.exe Only in boost/libs/python/test: hello.txt Only in boost/libs/python/test: voidptr Only in boost/libs/python/test: voidptr.cpp Only in boost/libs/python/test: voidptr.py Only in boost/tools/build/jam_src: bin.ntx86 Only in boost/tools/build/jam_src: bootstrap Only in boost/tools/build/jam_src: builtins.obj Only in boost/tools/build/jam_src: class.obj Only in boost/tools/build/jam_src: command.obj Only in boost/tools/build/jam_src: compile.obj Only in boost/tools/build/jam_src: execnt.obj Only in boost/tools/build/jam_src: execunix.obj Only in boost/tools/build/jam_src: execvms.obj Only in boost/tools/build/jam_src: expand.obj Only in boost/tools/build/jam_src: filent.obj Only in boost/tools/build/jam_src: fileos2.obj Only in boost/tools/build/jam_src: filesys.obj Only in boost/tools/build/jam_src: fileunix.obj Only in boost/tools/build/jam_src: filevms.obj Only in boost/tools/build/jam_src: glob.obj Only in boost/tools/build/jam_src: hash.obj Only in boost/tools/build/jam_src: hcache.obj Only in boost/tools/build/jam_src: hdrmacro.obj Only in boost/tools/build/jam_src: headers.obj Only in boost/tools/build/jam_src: jam.obj Only in boost/tools/build/jam_src: jambase.obj Only in boost/tools/build/jam_src: jamgram.obj Only in boost/tools/build/jam_src: lists.obj Only in boost/tools/build/jam_src: make.obj Only in boost/tools/build/jam_src: make1.obj Only in boost/tools/build/jam_src: modules.obj Only in boost/tools/build/jam_src: native.obj Only in boost/tools/build/jam_src: newstr.obj Only in boost/tools/build/jam_src: option.obj Only in boost/tools/build/jam_src: order.obj Only in boost/tools/build/jam_src: parse.obj Only in boost/tools/build/jam_src: path.obj Only in boost/tools/build/jam_src: pathunix.obj Only in boost/tools/build/jam_src: pathvms.obj Only in boost/tools/build/jam_src: property-set.obj Only in boost/tools/build/jam_src: pwd.obj Only in boost/tools/build/jam_src: regex.obj Only in boost/tools/build/jam_src: regexp.obj Only in boost/tools/build/jam_src: rules.obj Only in boost/tools/build/jam_src: scan.obj Only in boost/tools/build/jam_src: search.obj Only in boost/tools/build/jam_src: sequence.obj Only in boost/tools/build/jam_src: set.obj Only in boost/tools/build/jam_src: strings.obj Only in boost/tools/build/jam_src: subst.obj Only in boost/tools/build/jam_src: timestamp.obj Only in boost/tools/build/jam_src: variable.obj Only in boost/tools/build/jam_src: vc70.pdb Only in boost/tools/build/jam_src: w32_getreg.obj # Copyright Niall Douglas 2005. # Distributed under the Boost Software License, Version 1.0. # (See accompanying file LICENSE_1_0.txt or copy at # http://www.boost.org/LICENSE_1_0.txt) """ >>> from voidptr_ext import * Check for correct conversion >>> use(get()) Check that None is converted to a NULL void pointer >>> useany(get()) 1 >>> useany(None) 0 Check that we don't lose type information by converting NULL opaque pointers to None >>> assert getnull() is None >>> useany(getnull()) 0 Check that there is no conversion from integers ... >>> try: use(0) ... except TypeError: pass ... else: print 'expected a TypeError' ... and from strings to opaque objects >>> try: use("") ... except TypeError: pass ... else: print 'expected a TypeError' """ def run(args = None): import sys import doctest if args is not None: sys.argv = args return doctest.testmod(sys.modules.get(__name__)) if __name__ == '__main__': print "running..." import sys status = run()[0] if (status == 0): print "Done." sys.exit(status) The following section of this message contains a file attachment prepared for transmission using the Internet MIME message format. If you are using Pegasus Mail, or any other MIME-compliant system, you should be able to save it or view it from within your mailer. If you cannot, please ask your system administrator for assistance. ---- File information ----------- File: voidptr.cpp Date: 6 Nov 2005, 17:38 Size: 892 bytes. Type: Program-source

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Re: exporting __stdcall methods
by David Abrahams Feb. 11, 2006

Feb. 11, 2006

"John Maddock" <john(a)johnmaddock.co.uk> writes: >> Files like boost/type_traits/detail/is_mem_fun_pointer_tester.hpp >> which are outside the Boost.Python library would need to be enhanced >> to deal with __stdcall, etc. > > Should now be fixed in cvs: provided the changes don't break anything else > of course! Fantastic! Thanks, John! -- Dave Abrahams Boost Consulting www.boost-consulting.com

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