Mailman 3 August 2004 - 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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Pyste docstring support ?
by Kaben Nanlohy Sept. 2, 2004

Sept. 2, 2004

Hi; On this mailing list I have seen a patch to Boost.Python's Pyste providing some docstring support, but the patch does not appear to have been incorporated into cvs. Why is that ? Thanks -- K -- to contact me, use gmail.00(a)kaben.stochastic.net to contact me without your email entering my gmail archive, use no.gmail.00(a)kaben.stochastic.net

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ublas vector based arithmetic
by Neal D. Becker Sept. 1, 2004

Sept. 1, 2004

Recently I proposed using std::vector for arithmetic. Since then it was suggested to look at ublas. I think this is a good idea for my requirements. The intended application is 1) signal processinging/communications 2) vectors of int, double, complex 3) python for high level control to interface to c++ algorithms 4) c++ algorithms operate on relatively large vectors of data, so that overheads of python/c++ conversion are relatively unimportant. I agree that ublas would be a useful base, because the C++ algorithm side could be able to take advantage of the performance features, such as ET. I have gotten an implementation working, based mostly on Pylinear-0.9 from Andreas Kloeckner,ak(a)ixion.net, http://pylinear.sf.net. My version is much smaller, simpler and without all the dependencies, but only handles vectors (not matrices). It adds some convenience features, like constructing vectors from tuples/lists. If there is interest I can post.

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PyImport_Import problems with a BOOST_PYTHON_MODULE defined module
by Peter Aug. 29, 2004

Aug. 29, 2004

Thanks to some previous answers plus some intense googling, I've been able to use a C++ class to capture stdout and stderr. However, I have encountered a problem with PyImport_Import and a module defined with BOOST_PYTHON_MODULE. I created a StdoutCatcher C++ class (in a module named RuntimeSupport) and have got to the point where I can use it from within Python ok: >>> import sys, RuntimeSupport >>> sys.stdout = RuntimeSupport.StdoutCatcher() >>> sys.stderr = RuntimeSupport.StdoutCatcher() But my goal is to redirect stdout purely using the C APIs, but I still have much to learn and have hit a bit of a wall after experimenting all day. I found that PyImport_Import should accomplish what I want, but for all my experimenting I just can't get it to work. Below is the code and it would be great if anyone could critique my use of boost.python and the Python C API, and point out where I have gone wrong. All criticism would be very much appreciated. Building with MS VC++ 6 on w2k, using Python embedded in the app. //********************************************************* class StdoutCatcher { public: StdoutCatcher() { clear(); } void write( const std::string& str ) { text_ += str; } static const std::string& text(void) { return text_; } static void clear(void) { text_.erase(); } private: static std::string text_; }; std::string StdoutCatcher::text_; //********************************************************* // Python module BOOST_PYTHON_MODULE(RuntimeSupport) { class_<StdoutCatcher>("StdoutCatcher") .def( "write", &StdoutCatcher::write ) ; } ... initialize everything ... PyImport_AppendInittab("RuntimeSupport", initRuntimeSupport); Py_Initialize(); mainModule_ = new object(handle<>(borrowed( PyImport_AddModule("__main__") ) ) ); mainNamespace_ = new dict(mainModule_->attr("__dict__") ); ... everything now works ok if just using Python ... but I can't get it to work using just API calls, ... see below // import the RuntimeSupport module // --> I tried all import ways; // PyImport_ImportModuleEx, PyImport_Import, // PyImport_ImportModule boost::python::str supportModuleName("RuntimeSupport"); handle<> supportModule( PyImport_Import(supportModuleName.ptr()) ); // create an instance of StdoutCatcher // --> this bit doesn't work and returns NoneType // --> maybe because PyImport failed? object catcher = mainNamespace_->get("StdoutCatcher"); // --> is there a better way to check for NoneType // than a strcmp? PyObject* pObj = catcher.ptr(); if ( strcmp(pObj->ob_type->tp_name, "NoneType") == 0) { // ... why isn't StdoutCatcher being found? } else { // --> never get to this bit // create an instance of StdoutCatcher object catcherObj = catcher(); // set sys.stdout and sys.stderr to the // StdoutCatcher instance PySys_SetObject("stdout",catcherObj.ptr()); PySys_SetObject("stderr",catcherObj.ptr()); } ... so the main question is, why can't I import StdoutCatcher using the APIs? Thanks, Peter

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Re: [C++-sig] How to capture stdout/stderr?
by Peter Aug. 29, 2004

Aug. 29, 2004

Thanks Bert, that put on hopefully the right track to do the same thing in C++. I can almost do it completely, and I'll detail the code in another email. Thanks, Peter > > Here is my, considerably low-tech, code : > > At init time, > > ----------- > const std::string CatchOutput = > "class StdoutCatcher:\n" > "\tdef __init__(self):\n" > "\t\tself.data = ''\n" > "\tdef write(self, stuff):\n" > "\t\tself.data = self.data + stuff\n" > "\n" > "import sys\n" > "TheStdoutCatcher = StdoutCatcher()\n" > "sys.stdout = TheStdoutCatcher\n"; > > Run (CatchOutput); // thin wrapper to run a snippet > ----------- > > and then after some python code has run : > > ----------- > using namespace boost::python; > object Catcher (main_namespace ["TheStdoutCatcher"]); > object CatcherData (borrowed (PyObject_GetAttrString (Catcher.ptr (), > "data"))); > > const std::string &S = extract<std::string>(CatcherData); > Output += S; // some log string > Run ("sys.stdout.data=''\n"); > ----------- > > Note I'm pretty new at this, so the only warranty is > "the above didn't crash so far" :) Now that I paste > it, I'm not sure about that const ref to the result of > extract. > > > hth, > bert > > _______________________________________________ > C++-sig mailing list > C++-sig(a)python.org > http://mail.python.org/mailman/listinfo/c++-sig > >

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RE: [C++-sig] CXX : getting a C++ object
by Benjamin Golinvaux Aug. 28, 2004

Aug. 28, 2004

I have found the solution to my problem. The base class of the user-defined c++ python extension type provides a static bool check( PyObject* ) method that checks whether the object is of its kind. // somewhere : class MyExtensionType : public Py::PythonExtension<MyExtensionType> { ... } //somewhere else Object someFunctionExposedToPython(const Tuple &a) { Object o = a[0]; if(MyExtensionType::check(o.ptr())) { MyExtensionType* cppObj = static_cast<MyExtensionType*>(cppObj); // do something with cppObj } else { // it's not a MyExtensionType*, do something else } } (of course this isn't needed for MyExtensionType methods where "this" is automatically set correctly) this is exactly what i needed. hope this can help someone else (although it seems everyone here uses boost :) Benjamin -----Message d'origine----- De : c++-sig-bounces(a)python.org [mailto:c++-sig-bounces@python.org] De la part de Benjamin Golinvaux Envoyé : Saturday, August 28, 2004 11:48 PM À : Development of Python/C++ integration Objet : [C++-sig] CXX : getting a C++ object Hello I would like to wrap a small C++ library using CXX. I would like to know how I can extract the C++ instance from a PyObject passed to a function. Can I assume, after a correct type check, that I can safely downcast the PyObject ? (or using dynamic_cast ?) If I can't (or don't want to) use dynamic_cast , what could then be the best way to test that a PyObject is actually from a wrapped C++ "python type" class ? (sorry I'm a beginner in the Python C API) Thanks for your help Benjamin Golinvaux -------------------------------------------------------- The information contained in this message or any of its attachments may be privileged and confidential and intended for the exclusive use of the addressee. If you are not the addressee any disclosure, reproduction, distribution or other dissemination or use of this communication is strictly prohibited. If you have received this transmission by error please notify the sender immediately and then delete this email. EURESYS shall not be liable for any loss of or damage to revenues, profits, goodwill, data, information systems or other special, incidental, indirect, consequential or punitive damages of any kind arising in connection with the use of information contained in this mail or its attachments. Email transmission cannot be guaranteed to be secure or error free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore is in no way liable for any errors or omissions in the content of this message, which may arise as a result of email transmission. If verification is required, please request a hard copy. Please note that neither EURESYS, nor the sender accepts any responsibility for viruses and it is your responsibility to scan attachments (if any). -------------------------------------------------------- _______________________________________________ C++-sig mailing list C++-sig(a)python.org http://mail.python.org/mailman/listinfo/c++-sig -------------------------------------------------------- The information contained in this message or any of its attachments may be privileged and confidential and intended for the exclusive use of the addressee. If you are not the addressee any disclosure, reproduction, distribution or other dissemination or use of this communication is strictly prohibited. If you have received this transmission by error please notify the sender immediately and then delete this email. EURESYS shall not be liable for any loss of or damage to revenues, profits, goodwill, data, information systems or other special, incidental, indirect, consequential or punitive damages of any kind arising in connection with the use of information contained in this mail or its attachments. Email transmission cannot be guaranteed to be secure or error free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore is in no way liable for any errors or omissions in the content of this message, which may arise as a result of email transmission. If verification is required, please request a hard copy. Please note that neither EURESYS, nor the sender accepts any responsibility for viruses and it is your responsibility to scan attachments (if any). --------------------------------------------------------

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CXX : getting a C++ object
by Benjamin Golinvaux Aug. 28, 2004

Aug. 28, 2004

Hello I would like to wrap a small C++ library using CXX. I would like to know how I can extract the C++ instance from a PyObject passed to a function. Can I assume, after a correct type check, that I can safely downcast the PyObject ? (or using dynamic_cast ?) If I can't (or don't want to) use dynamic_cast , what could then be the best way to test that a PyObject is actually from a wrapped C++ "python type" class ? (sorry I'm a beginner in the Python C API) Thanks for your help Benjamin Golinvaux -------------------------------------------------------- The information contained in this message or any of its attachments may be privileged and confidential and intended for the exclusive use of the addressee. If you are not the addressee any disclosure, reproduction, distribution or other dissemination or use of this communication is strictly prohibited. If you have received this transmission by error please notify the sender immediately and then delete this email. EURESYS shall not be liable for any loss of or damage to revenues, profits, goodwill, data, information systems or other special, incidental, indirect, consequential or punitive damages of any kind arising in connection with the use of information contained in this mail or its attachments. Email transmission cannot be guaranteed to be secure or error free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore is in no way liable for any errors or omissions in the content of this message, which may arise as a result of email transmission. If verification is required, please request a hard copy. Please note that neither EURESYS, nor the sender accepts any responsibility for viruses and it is your responsibility to scan attachments (if any). --------------------------------------------------------

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Re: [C++-sig] Instantiating a Python class from C++?
by Peter Aug. 28, 2004

Aug. 28, 2004

That worked wonderfully, thank you. I did have to make a small change to accomadate VC++ 6: module_namespace["DerivedClass"] changed to module_namespace.get("DerivedClass") > I will suppose you have access to the module namespace containing the > derived class. I'll call this "module_namespace". So, you can retrieve > the class using Boost.Python very simply : > > boost::python::object cls = module_namespace["DerivedClass"] > > And now, you can create the object with : > > boost::python::object obj = cls(); > > And to get a pointer to the underlying C++ object : > > MyClass* cpp_obj = extract<MyClass*>(obj); > > It should work ... > > Pierre > > Peter a écrit : > > Another question, and I really hope this doesn't get emailed four > > idnetical times like my last question. My sincere apologies in advance > > if it does. > > > > I have a C++ class with a virtual function that I want overridden in > > Python. I expose it to Python in the normal way: > > > > class_<MyClass>("CPP_Class", no_init) > > .def("vfunc", &MyClass::func); > > > > And in Python the user derives from this class overrides the virtual > > method, e.g.: > > > > class DerivedClass(CPP_Class): > > def vfunc(self): > > #do stuff in Python > > > > I want to create an instance of "DerivedClass" from C++ and assign it to > > the base class ptr and then call the overridden Python function via the > > virtual fn defined in the C++ base class. So my question is; how do I, > > from C++, create this instance of DerivedClass (assuming I know that the > > user called it DerivedClass)? > > > > Thank you very much for any help, > > Peter > > > > > > > > > > > > > > _______________________________________________ > > C++-sig mailing list > > C++-sig(a)python.org > > http://mail.python.org/mailman/listinfo/c++-sig > > > > -- > Pierre Barbier de Reuille > > INRA - UMR Cirad/Inra/Cnrs/Univ.MontpellierII AMAP > Botanique et Bio-informatique de l'Architecture des Plantes > TA40/PSII, Boulevard de la Lironde > 34398 MONTPELLIER CEDEX 5, France > > tel : (33) 4 67 61 65 77 fax : (33) 4 67 61 56 68 > _______________________________________________ > C++-sig mailing list > C++-sig(a)python.org > http://mail.python.org/mailman/listinfo/c++-sig > >

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Instantiating a Python class from C++?
by Peter Aug. 28, 2004

Aug. 28, 2004

Another question, and I really hope this doesn't get emailed four idnetical times like my last question. My sincere apologies in advance if it does. I have a C++ class with a virtual function that I want overridden in Python. I expose it to Python in the normal way: class_<MyClass>("CPP_Class", no_init) .def("vfunc", &MyClass::func); And in Python the user derives from this class overrides the virtual method, e.g.: class DerivedClass(CPP_Class): def vfunc(self): #do stuff in Python I want to create an instance of "DerivedClass" from C++ and assign it to the base class ptr and then call the overridden Python function via the virtual fn defined in the C++ base class. So my question is; how do I, from C++, create this instance of DerivedClass (assuming I know that the user called it DerivedClass)? Thank you very much for any help, Peter

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How to capture stdout/stderr?
by Peter Aug. 28, 2004

Aug. 28, 2004

Hi, I am trying to capture stdout and stderr from Python using boost.python. I can do it using the Python C API but can't work out the correct way to do it using the boost wrappers. Using the C API I'd do something like: PyObject* pObj = Py_InitModule("stdout", my_methods); PySys_SetObject("stdout", pObj); PySys_SetObject("stderr", pObj); How should I do this with boost? Thanks Peter

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