Mailman 3 September 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

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Two Pyste suggestions
by Niall Douglas Oct. 6, 2003

Oct. 6, 2003

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Yeah, more ideas! The first is a bit radical. I've organised the policies for my project into a python package called "Policies". Within it is a .py file for every class in my library and within each of those is an apply() method. In the pyste files, each class imports its policy from Policies.<classname> and calls Policies.<classname>.apply(). This in turn imports the policy .py files for each of the base classes the class inherits from and calls their apply() methods first before setting its own policies for its own local class. Thus you see a change to a base class automatically propagates through the policy hierarchy. Now my suggestion is that since pyste knows what classes any class inherits, it could spit out the import's and apply()'s for each policy for class. It would save some work (I've already done it manually, wish I'd thought of it sooner). The second suggestion was as I made last time, a --files parameter to specify a file from which to read the list of pyste files as Win2k has a 2Kb limit. I've attached the pyste.py file for an example. Cheers, Niall -----BEGIN PGP SIGNATURE----- Version: idw's PGP-Frontend 4.9.6.1 / 9-2003 + PGP 8.0.2 iQA/AwUBP3hjPsEcvDLFGKbPEQJanACg8exEBe66enOWYGcMeMEAh1bXbF4An1QO BYYW2KwFEC8mV+ITYUtJAKxz =4Y4o -----END PGP SIGNATURE-----

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RE: [C++-sig] Bug: Pyste misoutputs 64 bit ints on MSVC
by Conan Brink Oct. 6, 2003

Oct. 6, 2003

There appear to be boost::int64_t and boost::uint64_t in <boost/cstdint.hpp>, as part of the integer library, for those systems where they are not already defined in <stdint.h> (cstdint.hpp will include stdint.h if it is available, or typedef the various integer types for itself if not) -Conan -----Original Message----- From: Niall Douglas [mailto:s_sourceforge@nedprod.com] Sent: Monday, September 22, 2003 3:26 PM To: c++-sig(a)python.org Subject: Re: [C++-sig] Bug: Pyste misoutputs 64 bit ints on MSVC -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 21 Sep 2003 at 14:34, Nicodemus wrote: > >Obviously this would break GCC. Nicodemus I think you'll need a -- > >msvc switch which lets you switch in MSVC specific output. > > Seems like so, unfortunately. How about a --msvc command line switch? Actually I had a thought on this. Doesn't Boost provide a macro resolving to a signed and unsigned 64 bit int? Cheers, Niall This message contains information that may be confidential and privileged. Unless you are the addressee (or authorized to receive messages for the addressee), you may not use, copy, or disclose to anyone the message or any information contained in the message. If you have received the message in error, please advise the sender by reply e-mail and delete the message. Nothing in this message should be interpreted as a digital or electronic signature that can be used to authenticate a contract or any other legal document.

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Boost.Python : Byref parameters
by Joel Gerard Oct. 6, 2003

Oct. 6, 2003

Hi All, I'm trying to call a C++ member function from Python that takes three ints by reference, and modifies them. static f32 Normalize (f32& fx, f32& fy, f32& fz); Furthermore, its overloaded: f32 Normalize (void); static f32 Normalize (Vector& kV); I've wrapped it like so: f32 (Vector::*VectorNormalize1)(void) = &Vector::Normalize; f32 (*VectorNormalize2)(Vector&)= &Vector::Normalize; f32 (*VectorNormalize3)(f32&,f32&,f32&) = &Vector::Normalize; .def("Normalize",VectorNormalize1) .def("Normalize",VectorNormalize2) .def("Normalize",VectorNormalize3) Only Normalize defined by VectorNormalize3 is broken saying: "TypeError: unbound method Boost.Python.function object must be called with Vector instance as first argument (got float instance instead)" I think I'm doing something wrong with the call-policies (since I have none), but I don't know which ones to use. What am I doing wrong? Can somebody explain what Boost is trying to do here? Thanks, Joel ===== -------------------------------------- Email: joelgerard(a)canada.com __________________________________ Do you Yahoo!? The New Yahoo! Shopping - with improved product search http://shopping.yahoo.com

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(no subject)
by Andrew Ellem Sept. 30, 2003

Sept. 30, 2003

I am having problems with Boost.Python (attempting to) delete classes passed to it. This is being done in the Battle constructor (which is invoked from C++). I'm basing my work off the embedding.cpp example, and I am creating the Python-derived class like this: (Where Script is a .py file and Script.Standard is derived from the Script in the Battle module below). [...] handle<> class_ptr( PyRun_String("Script.Standard\n", Py_eval_input, main_namespace.get(), main_namespace.get()) ); object PythonDerived(class_ptr); object py_base = PythonDerived(this); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This line is the problem [...] My module is defined like this: BOOST_PYTHON_MODULE(Battle) { class_<Battle>("Battle", no_init) .def("GetHandle", &Battle::GetHandle) ; class_<Script, ScriptWrapper, boost::noncopyable> ("Script", init<Battle*>()) ; } The PythonDerived constructor is called successfully (it prints, etc). However in the PythonDerived(this) call, I get error about an invalid HANDLE, in the Boost.Python instance_dealloc function at the line 284 of class.cpp: instance_holder::deallocate(inst, dynamic_cast<void*>(p)); It seems that Boost is trying to delete the Battle class that is being passed to it. Is this correct? How do I prevent this? I tried adding return_value_policy<reference_existing_object>() to the init<> of Script, but it didn't' seem to change anything. Is this even what I want to do? I also tried to add boost::noncopyable to my definition of Battle, in hopes that it would prevent this, but then I would get errors about no to_python converter. I guess that I'm a little confused as to what exactly is going on, and how to go about fixing it. Thanks, Andrew

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vector_indexing_suite too defensive ...
by Mike Thompson Sept. 30, 2003

Sept. 30, 2003

I've found a small difference between the behaviour of python lists and vector's wrapped by using the talented vector_indexing_suite. Let's say I write a python function which forces a list to be a particular size by padding it (if below the required size), or chopping it down (if above the required size): >>> def padOrChop(lst, size, padValue=0): ... diff = size- len(lst) ... lst[size:] = [padValue] * diff ... This function work nicely with normal python lists .... >>> >>> L = [2, 3, 4, 5] >>> padOrChop(L, 10) >>> L [2, 3, 4, 5, 0, 0, 0, 0, 0, 0] >>> padOrChop(L, 2) >>> L [2, 3] >>> but it will fail with an object created through vector_indexing_suite whenever it has to pad: >>> L = IntVec() # really a vector<int> >>> L[:] = [2, 3, 4, 5] >>> padOrChop(L, 10) Traceback (most recent call last): File "<stdin>", line 1, in ? File "<stdin>", line 3, in padOrChop IndexError: Index out of range >>> padOrChop(L, 2) >>> [i for i in L] [2, 3] >>> The IndexError arises because vector_indexing_suite defends against an slice index being too big, rather than the python list approach which regards a slice index > len(L) as equal to len(L). So, the line of padOrChop() which says: lst[size:] = [padValue] * diff causes an exception when size > len(lst). Should vector_indexing_suite be altered to give behaviour more like that of lists in this regard? -- Mike

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On wrapping vector<pair<string, double> >
by Zhang Le Sept. 30, 2003

Sept. 30, 2003

Hello, I'm trying to wrap a function that takes a vector<pair<string, double> > as input and return a list. The original function is vector<double> eval(const vector<pair<string, double> >&); to use boost python, I write a wrapper function: python::list py_eval(python::tuple input) { here I want to use python::extract<std::string>(input[i][0]) and python::extract<double>(py_context[i][1]) to transform python input [('A', 1.0), ('B', 2.0), ...] into a new vector<pair<string, double> > for calling real eval() } Compilation is ok and I get an error in python code: obj.py_eval([('A', 1.0), ('B', 2.0)]) TypeError: No registered converter was able to produce a C++ rvalue of type j from this Python object of type str I change the declaration to python::list input, python::object input and get the same error result. Am I missing anything? -- Sincerely yours, Zhang Le

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constructing datetime objects
by gero_mailinglist＠gmx.de Sept. 30, 2003

Sept. 30, 2003

Hi, I am pretty new to boost python and consider integrating an existing C++ library into python 2.3. My C++ library defines its own datetime class, but I think it is nicer if the python functions use the Python datetime module. How do I write a function that returns a python datetime object, initialised e.g. via an ordinal number or maybe year, month, day, etc. I have not found out yet how to call a constructor in boost::python (Is there something in the tutorial?). The other way, e.g. getting the year from a python datetime object dt is no problem using python::extract<int>(dt.attr("year")). Thanks in advance, Gero -- NEU FÜR ALLE - GMX MediaCenter - für Fotos, Musik, Dateien... Fotoalbum, File Sharing, MMS, Multimedia-Gruß, GMX FotoService Jetzt kostenlos anmelden unter http://www.gmx.net +++ GMX - die erste Adresse für Mail, Message, More! +++

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return_existing_reference
by Niall Douglas Sept. 29, 2003

Sept. 29, 2003

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Out of interest (couldn't find this in the docs), if the C++ code returns a NULL pointer does Boost.Python translate this under return_existing_reference and return_internal_reference as None? Cheers, Niall -----BEGIN PGP SIGNATURE----- Version: idw's PGP-Frontend 4.9.6.1 / 9-2003 + PGP 8.0.2 iQA/AwUBP3hpC8EcvDLFGKbPEQKhfQCgoPqXSXVeFApiKOexfAgP11yV0kMAoI6D Lnma/g7MR46TAD0m4Py5Lz7z =1Yrs -----END PGP SIGNATURE-----

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python-list to c++-vector
by Lars Kunert Sept. 29, 2003

Sept. 29, 2003

Hi! Is this here really the easiest and the fastest way to transfer a small (<10000) python-list of integers into a std::vector?! #include <boost/python.hpp> #include <vector> #include <iostream> class Ints { private: std::vector<int> _ints; public: void set( boost::python::object o ) { boost::python::list list = boost::python::extract<boost::python::list>(o); try { _ints.clear(); bool is_ok = true; while( is_ok ) { boost::python::extract<int> x( list.pop( 0 )); if( x.check()) { _ints.push_back( x()); } else { is_ok = false; }; }; } catch ( ... ) { std::cerr << "exception thrown"; }; }; }; // Using ======================================================================= using namespace boost::python; // Module ====================================================================== BOOST_PYTHON_MODULE(Iterator_module) { class_< Ints >("Ints", init<>()) .def("set", &Ints::set ) ; };

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