Mailman 3 May 2008 - Cplusplus-sig

Exposing C++ Functions with Container Arguments in Boost.Python
by Bilokon, Paul May 11, 2008

May 11, 2008

Hi all, This is probably a trivial question, but after some research I was unable to find a "best practice" answer, so my sincere apologies. I am trying to expose a C++ function which takes an std::vector<double> as its argument, some void A::foo(std::vector<double> v); And perhaps void A::bar(std::vector<double> & v); Whether it is a good practice to have such arguments is, of course, open to debate (shouldn't they be iterators?), but this is what I have to work with. The question remains, what is the best way to expose these to python? I cannot pass a Python list -- it's a type mismatch. Many thanks! Regards, Paul - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - This message is intended only for the personal and confidential use of the designated recipient(s) named above. If you are not the intended recipient of this message you are hereby notified that any review, dissemination, distribution or copying of this message is strictly prohibited. This communication is for information purposes only and should not be regarded as an offer to sell or as a solicitation of an offer to buy any financial product, an official confirmation of any transaction, or as an official statement of Lehman Brothers. Email transmission cannot be guaranteed to be secure or error-free. Therefore, we do not represent that this information is complete or accurate and it should not be relied upon as such. All information is subject to change without notice.

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Embedded Python Terminal Output
by Thomas Hrabe May 9, 2008

May 9, 2008

Hi all, I was wandering how one could catch the terminal output of an embedded python interface? Errors are beautifully displayed in the terminal of the caller program, and each python print command, but I want the output when I type only >>> 1 Regards, Thomas

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Problem embedding Python with Boost.Python
by David Walker May 8, 2008

May 8, 2008

Hi, I'm trying to embed python in an add-in library (actually a DLL ). I'm starting from the example in embedding.cpp, overriding the C++ base class in Python then calling that overridden method from C++. I'm now in the situation where the code works OK in debug, but not in release. The call stack is showing the point of failure to be in the conversion of the python object to the object reference which results from the second line of this snippet - boost::python::object py_base = pyderived(); PyTestFunc2& py = boost::python::extract<PyTestFunc2&>(py_base); Has anyone any ideas ? I have tried building a cut-down example but annoyingly that works in both release and debug mode. I'm assuming that something in my library is interfering with the boost.python calls (but I'm only explicitly calling the python stuff in my test, so the interaction presumably takes place when some static initialization is being done) - has anyone else seen this sort of thing ? Thanks, David ********************************************************** Mitsubishi UFJ Securities International plc ("MUSI") is registered in England, company number 1698498, registered office at 6 Broadgate, London EC2M 2AA, and is part of the Mitsubishi UFJ Financial Group. MUSI is authorised and regulated in the UK by The Financial Services Authority Limited (FSA). The information contained herein or attached hereto has been obtained from sources we believe to be reliable but we do not represent that it is accurate or complete and is not to be viewed as a 'personal recommendation' within the meaning of the FSA rules. The Information is not to be construed as an offer or solicitation to buy or sell any security, instrument or investment. Any reference to past performance should not be taken as an indication of future performance. MUSI or any affiliated company may have an interest, position, or effect transactions, in any investment mentioned herein. Any opinions or recommendations expressed herein are solely those of the author or analyst and are subject to change without notice. Neither MUSI nor any of its affiliates accept any liability whatsoever for any direct or consequential loss arising from any use of information or material contained herein. This message is intended solely for the individual addressee named above. The information contained in this e-mail is confidential and may be legally privileged. If you are not the intended recipient, you must not copy, distribute or take any action in reliance on it. Messages sent via this medium may be subject to delays, non-delivery and unauthorised alteration.

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Embedding Python - data exchange && no Boost
by Thomas Hrabe May 7, 2008

May 7, 2008

Hi all, I am writing an embedded python application in C/C++ with the following features: 1. The user is able to execute python commands (works fine with PyRun_SimpleString) 2. I want the user to be able to load C objects from C into the current python interpreter, so that the user is able to manipulate the python copies with python tools -> no go. I first wrote a function within a module which is loaded after Py_Initialize(), returning an PyObject. I thought it might be possible to share a static variable between the module and the C application, where the module function could access the static variable, convert it to a PyObject and provide it to the interpreter. Think of this procedure in terms of python calls: import PA; //imports the module in the embedded interpreter a = PA.set() ; //access the static object, create a PyObject, return it as a The later python calls should be able to manipulate a and then return it back to C by setting the static object again like PA.get(a) ; //or similar However, it turned out that the static object in the interpreter differs from the one in the C program -> other adresses in memory, so that I can not share the memory space. Does anybody know of a solution for such a problem? Any tips? I do not use Boost because the program is supposed to process numpy's nd-arrays and, furthermore, must remain independent of additional libraries such as Boost. I'd use it otherwise... Thank you in advance for your help, Thomas

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Problem with boost.python 1.35.0
by Grant Tang May 7, 2008

May 7, 2008

My application works fine with previous versions of boost.python. But I tried to compile it with the boost.python 1.35.0, it fails with the compilation. Can some one help me? /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/type_traits/detail/cv_traits_impl.hpp: In instantiation of 'const bool boost::detail::cv_traits_imp<<unnamed>::EMAN_Aligner_Wrapper*>::is_const': /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/type_traits/is_const.hpp:53: instantiated from 'boost::is_const<<unnamed>::EMAN_Aligner_Wrapper>' /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/python/detail/cv_category.hpp:31: instantiated from 'boost::python::detail::cv_category<<unnamed>::EMAN_Aligner_Wrapper>' /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/python/detail/unwind_type.hpp:58: instantiated from 'typename Generator::result_type boost::python::detail::unwind_ptr_type(U*, Generator*) [with Generator = boost::python::converter::detail::unwind_type_id_helper, U = <unnamed>::EMAN_Aligner_Wrapper]' /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/python/detail/unwind_type.hpp:127: instantiated from 'static typename Generator::result_type boost::python::detail::unwind_helper2<2>::execute(U& (*)(), Generator*) [with Generator = boost::python::converter::detail::unwind_type_id_helper, U = <unnamed>::EMAN_Aligner_Wrapper]' /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/python/detail/unwind_type.hpp:165: instantiated from 'typename Generator::result_type boost::python::detail::unwind_type(boost::type<U>*, Generator*) [with Generator = boost::python::converter::detail::unwind_type_id_helper, U = <unnamed>::EMAN_Aligner_Wrapper&]' /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/python/converter/pytype_function.hpp:45: instantiated from 'boost::python::type_info boost::python::converter::detail::unwind_type_id_(boost::type<Target>*, mpl_::false_*) [with T = <unnamed>::EMAN_Aligner_Wrapper&]' /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/python/converter/pytype_function.hpp:68: instantiated from 'static const PyTypeObject* boost::python::converter::expected_pytype_for_arg<T>::get_pytype() [with T = <unnamed>::EMAN_Aligner_Wrapper&]' /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/python/detail/signature.hpp:98: instantiated from 'static const boost::python::detail::signature_element* boost::python::detail::signature_arity<5u>::impl<Sig>::elements() [with Sig = boost::mpl::v_item<void, boost::mpl::v_item<<unnamed>::EMAN_Aligner_Wrapper&, boost::mpl::v_mask<boost::mpl::v_mask<boost::mpl::vector6<EMAN::EMData*, EMAN::Aligner&, EMAN::EMData*, EMAN::EMData*, const std::string&, const EMAN::Dict&>, 1>, 1>, 1>, 1>]' /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/python/detail/caller.hpp:232: instantiated from 'static boost::python::detail::py_func_sig_info boost::python::detail::caller_arity<5u>::impl<F, Policies, Sig>::signature() [with F = boost::python::detail::nullary_function_adaptor<void (*)()>, Policies = boost::python::default_call_policies, Sig = boost::mpl::v_item<void, boost::mpl::v_item<<unnamed>::EMAN_Aligner_Wrapper&, boost::mpl::v_mask<boost::mpl::v_mask<boost::mpl::vector6<EMAN::EMData*, EMAN::Aligner&, EMAN::EMData*, EMAN::EMData*, const std::string&, const EMAN::Dict&>, 1>, 1>, 1>, 1>]' /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/python/object/py_function.hpp:48: instantiated from 'boost::python::detail::py_func_sig_info boost::python::objects::caller_py_function_impl<Caller>::signature() const [with Caller = boost::python::detail::caller<boost::python::detail::nullary_function_adaptor<void (*)()>, boost::python::default_call_policies, boost::mpl::v_item<void, boost::mpl::v_item<<unnamed>::EMAN_Aligner_Wrapper&, boost::mpl::v_mask<boost::mpl::v_mask<boost::mpl::vector6<EMAN::EMData*, EMAN::Aligner&, EMAN::EMData*, EMAN::EMData*, const std::string&, const EMAN::Dict&>, 1>, 1>, 1>, 1> >]' /home/g/EMAN2/src/eman2/libpyEM/libpyAligner2.cpp:358: instantiated from here /home/g/library/boost_1_35_py2.5.ucs4/include/boost-1_35/boost/type_traits/detail/cv_traits_impl.hpp:37: internal compiler error: in make_rtl_for_nonlocal_decl, at cp/decl.c:5067 Please submit a full bug report, with preprocessed source if appropriate. See <URL:http://bugzilla.redhat.com/bugzilla<http://bugzilla.redhat.com/bugzilla>> for instructions. Preprocessed source stored into /tmp/cc2yhNUv.out file, please attach this to your bugreport. make[2]: *** [libpyEM/CMakeFiles/pyAligner2.dir/libpyAligner2.o] Error 1 make[1]: *** [libpyEM/CMakeFiles/pyAligner2.dir/all] Error 2 make: *** [all] Error 2 Grant

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Error when trying to embed python into C++
by Erin Stone May 7, 2008

May 7, 2008

Hi - I'm a newbie to doing this and would appreciate any help / suggestions. Here's my problem, I have an existing python application and a 3rd party C++ dll that need to talk to each other. So far I have been able to follow the "Extending and Embedding Python" tutorial to create an extension to make the C++ dll available to my python app and have it (the extension) return back values (ints, strings, etc) to the python app. The 3rd party dll has one method that I need to use that requires a callback with a particular signature. My thinking is as follows: 1. create callback method in my python module 2. create a method in my C++ extension that would take as a parameter the method from step 1 and store it 3. create another method in my C++ extension that would act as the 3rd party dll callback with the particular signature 4. set the method in #3 to be the callback for the 3rd party dll 5. when the method in #3 is called back to from the 3rd party, parse the data into appropriate python objects and then call the python callback from #2 Problem is when I do this, I get a python.exe error and my application crashes - so any ideas on what I am missing?? I don't have the option of using boost because this is a legacy application and do cannot introduce another framework. Again, any help is appreciated! Thanks, Erin Here is the code: Python import wx import camera_ext #this is the C++ ext class frmMain(wx.Frame): def _init_ctrls(self, prnt): #we just initialize the controls on the form here def __init__(self, parent): self._init_ctrls(parent) def OnInstallHooker(self, event): installed = camera_ext.InstallFrameHooker(self._my_frame_hooker) # is this right? Or should it be a module method, not a method of the class? self.txtData.SetValue("installed hooker: " + str(installed)); def OnStartGrab(self, event): started = camera_ext.StartFrameGrab() self.txtData.SetValue("started grabbing: " + str(started)); def _my_frame_hooker(self): # should be called from the c++ ext print "I was called" # this never gets printed out ???? return True C++ (camera_ext) static void FrameCallBack( TProcessedDataProperty* Attributes, unsigned char *Frameptr ) { //once called, we need to package up to return it to python as an actual object PyObject *arglist; PyObject *result; printf("foo") //this does print out so I know the 3rdparty dll (BUFUSB is calling back) // All frame data is pointed by Frameptr // All frame related attributes is in Attributes. arglist = Py_BuildValue("i", Attributes->CameraID); result = PyObject_CallObject(my_python_callback,arglist); Py_DECREF(arglist); } static PyObject *install_frame_hooker(PyObject *dummy, PyObject *args){ int retVal = 0; PyObject *result = NULL; PyObject *tobj; if (!PyArg_ParseTuple(args, "O:set_callback", &tobj)) return NULL; // make sure second argument is a function if (!PyCallable_Check(tobj)) { PyErr_SetString(PyExc_TypeError, "Need a callable object!"); } Py_XINCREF(tobj); /*add a reference to the new callback instance*/ Py_XDECREF(my_python_callback); /*dispose of previous callback instance */ my_python_callback = tobj; /*save reference to new callback instance */ Py_INCREF(Py_None); result = Py_None; /*now this method must call the camera's SDK InstallFrameHooker to install the C++ FrameHooker - note that 0 is raw data, 1 is bmp data */ retVal = BUFUSB_InstallFrameHooker(0, FrameCallBack); return result; } static PyObject *start_frame_grab(PyObject *self, PyObject *args){ //starts grabbing data int retVal = 0; //start frame grab will cause camera engine to call on the frame hooker (callback) method to return camera data retVal = BUFUSB_StartFrameGrab(0x8888); return Py_BuildValue("i", retVal); } static PyMethodDef camera_ext_methods[] = { {"StartFrameGrab", start_frame_grab, METH_VARARGS, "Start grabbing frames, specify the number of frames to grab"}, {"InstallFrameHooker", install_frame_hooker, METH_VARARGS, "Set the callback function to notify caller everytime the camera engine gets a new frame"}, {NULL, NULL} }; void initcamera_ext(void) { import_array(); Py_InitModule("camera_ext", camera_ext_methods); }

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Spirit Python bindings
by Alex Klizhentas May 7, 2008

May 7, 2008

Hi All, Are there any Python bindings for Spirit you are aware of? Thanks in advance, Alex

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May 6, 2008

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Boost::Python - Question about object ownership and lifetime
by Mike Stoddart May 6, 2008

May 6, 2008

Hi folks, new to Boost Python and struggling to build a prototype at work. I thought I'd start with a conceptual question to help clarify my understanding. I already have a basic prototype working nicely but I'm having a few issues, which I may post about later. A brief functional rundown of what I'm trying to prototype. Hopefully my explanation doesn't get too confusing! I'm embedding a python module into an application; Python will provide application logic, responding to events such as timers expiring or the user clicking widgets. I have the following classes I'm exporting to Python: Entity, DerivedEntity, EntityList (contains pointers to Entity). They all have varying types of copy/constructors, e.g. some are private, some have non-const copy constructors etc. It's inherited code that I can't mess with so I'm stuck with it. So the typical logic flow I'm looking at is: C++ Application: - Create an instance of EntityList called entity_list, populate with many instances of DerivedEntity. - Create an instance of EntityList called change_list - Invoke python function passing entity_list and change_list as parameters Python: - For each entity in entity_list: - Invoke C++ function clone_entity, pass entity as parameter C++ Application: - Create clone of entity like this --> DerivedEntity* entity_copy = new DerivedEntity(entity) - return entity_copy to Python Back in Python again: - Apply logic to entity_copy returned from clone_entity C++ function - If entity_copy updated add to change_list Back in C++ Application: - For each new_entity in change_list - Apply further logic to new_entity - Delete new_entity pointer - Clear the change_list I'm having problems in my prototype - it looks like I have a memory leak but I'm not sure where. So my question is, what should I be aware of in this logic flow with regards to object ownership and lifetime? When I receive entity_copy in Python, returned from clone_entity, what happens to this object when I insert it into change_list and subsequently delete the C++ pointer? I don't know how to prove that the Python object is being deleted and isn't hanging around due to a lifetime issue, I guess my main problem is that I'm entirely sure I understand object ownership - who owns what object when it's created in C++, passed to Python and then returned back to C++ to be deleted. So if any of this makes sense, I would greatly appreciated any suggestions or help. I'm very impressed with Boost Python so far but my own lack of understanding is holding me back I think. Thanks again Mike

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Boost.Python and std::string subclassing
by Pertti Kellomäki May 5, 2008

May 5, 2008

The library I am wrapping creates a subclass TCEString of std::string. Py++ generates me bindings for the subclass, but in Python the subclass does not quite work like std::string. For example, the Python expression "%s.%s.%s" % (term.functionUnit().name(), term.port().name(), term.operation().name()) returns the string "universal_fu.OCSetting32.<TCE.tools.TCEString object at 0x81308ec>" because term.operation().name() returns a TCEString instead of std::string. Is there some convenient way to make the subclass work like std::string? I know how to do it by defining a __str__ method in the Python class, but I am hoping that there might be a simpler way to do it using Boost.Python or Py++. -- Pertti

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