Mailman 3 October 2002 - Cplusplus-sig

(no subject)
by James Webster Oct. 25, 2002

Oct. 25, 2002

confirm 502702

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linking with external libraries
by Leonardo Rochael Almeida Oct. 24, 2002

Oct. 24, 2002

Hi, As I mentioned before, I'm wrapping a GIS library. This library build process can't be easily boostified, so it is built externally and I have to instruct my extensions to link against it and to search for include files in specific locations. My first try to make this run on Linux went like this (Jamfile): extension pyterralib : # sources pyterralib.cpp # dependencies <dll>../build/boost_python : # requirements <sysinclude>/usr/local/include/terralib <linkflags>-lterralib ; And it worked reasonably well, but it left me unsatisfied. the <sysinclude> feature seems reasoable, but I felt there should be a more generic way to specify a library to link against instead of a specific <linkflags>. Sure enough, when I tried to make the same thing work in Windows, "<linkflags>-l" wouldn't cut it, so I found the <library-path> and <library-file> features which, in msvc-tools.jam seemed to do the right thing, so I did this: # Declare a Python extension called geobusca extension pyterralib : # sources pyterralib.cpp # dependencies <dll>../build/boost_python : # flags <sysinclude>C:/geobusca/terralib/Terralib10/src/terralib <library-path>C:/geobusca/terralib/Terralib10/terralibw/terralib/Debug <library-file>terralib ; Unfortunately this doesn't work as bjam complains: don't know how to make terralib the <sysinclude> part works, without it the build failed in the middle of the compilation, but I don't know the proper link flags for msvc (I'm a Linux guy) and I was hoping boost.build would free me from ever having to learn it :-) So is there an official and cross-platform way to specify a dependency on an external library which boost.build shouldn't try to build? Cheers, Leo -- Ideas don't stay in some minds very long because they don't like solitary confinement.

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Re: ANN: Boost.Python v2
by David Abrahams Oct. 23, 2002

Oct. 23, 2002

Joe Van Andel <vanandel(a)atd.ucar.edu> writes: > Thanks for your quick response. No problem. > > http://www.boost.org/libs/python/doc/v2/numeric.html > > > Sorry, I guess I missed this. You do reference Numeric in the > reference manual, but I didn't see any reference in the Synopsis or > the Tutorial Introduction. Would you be willing to mention Numeric > support in the Synopsis? Sure. Tell me what you think it should say. > Do you have any more examples of accessing Numeric arrays using Boost? http://www.boost.org/libs/python/test/numpy.cpp http://www.boost.org/libs/python/test/numpy.py > >>That is, I want to pass Numeric Python arrays to my C++ extensions, > >>and not have to write my C++ code to be aware of the Numeric > >>interfaces (if possible). > > I'm not sure what you mean by "not aware of the Numeric interfaces". > > Sorry, I meant to say the Numeric API, e.g. calls like: > PyArray_ISCONTIGUOUS() > or > PyArray_As2D((PyObject **)&theInput, (char ***)&inP, > &numRays, &numGates, PyArray_FLOAT); I don't know if the above meets your needs. The numeric support could use some fleshing-out, as others have pointed out on this list. Patches to enhance the existing numeric support would be gratefully considered. HTH, -- David Abrahams dave(a)boost-consulting.com * http://www.boost-consulting.com Building C/C++ Extensions for Python: Dec 9-11, Austin, TX http://www.enthought.com/training/building_extensions.html

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splitting it into multiple pieces
by greg Landrum Oct. 23, 2002

Oct. 23, 2002

Today while trying to build my BPLv2 stuff under windows using MSVC++, I got this beauty of an error: >compiler limit : internal structure overflow > >The compiler has run out of memory. Your program needs to be simplified, >perhaps by splitting a large source code file into smaller files. (explanation from http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccore/htm…) I've been thinking about splitting my project up into multiple files anyway; I guess this is MSVC's way of telling me that the time has come. Now I just need to figure out how. The problem is that I've got a bunch of interconnected objects: Molecules are made up of Atoms and Bonds (and have GetAtom/Bond methods) Atoms and Bonds each contain a pointer back to their parent Molecule (and have GetParent methods) I'd like to have separate modules for Mols, Atoms and Bonds. Can I do this given the interdependencies? If so, is there a convenient example laying around somewhere I can look at/steal code from? thanks, -greg

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wrapping global variables
by Dominique Devriese Oct. 20, 2002

Oct. 20, 2002

Hi, ( please cc me as i'm not subscribed to the list) I'm playing around a bit with embedding python in a C++ program. I'm using Boost.python for exposing the program's API to python, and the normal python interface ( Py_Initialize, PyRun_SimpleString and Py_Finalize ) for embedding. So far this has proven surprisingly easy. Especially Boost.Python has amazed me with its ease of use, so congratulations to everyone here who helped write it, as it most definitely rocks :) But I have a question: I would like to expose some global variables to python. E.g. if I have a variable curbuf, I would like to be able to write ( in the embedded python interpreter, that is ) something like "len = curbuf.length();". curbuf is of class Buffer, and this class has been exported very easily, but I don't seem to be able to find how to expose a global variable. Of course I can think of some workarounds like exposing a free function, exposing a curbuf class that has a singleton constructor, combining either of the above with something like "PyRun_SimpleString( \"global a = freeFunOrClass();\" );" ( If that is wrong python, that's because I'm more of a C++ programmer than a python programmer ;) etc., but I was wondering if there wasn't a clean way to go about it. I've browsed the c++-sig(a)python.org archives a bit ( but as there doesn't seem to be a search function, I've only read the last five months or so ), and all i've found was this thread: http://mail.python.org/pipermail/c++-sig/2002-July/001768.html but it's not very clear... So, is there a way to do this, or are there any plans to implement it any time soon or are there any easy alternatives I'm missing ? Thanks in advance domi -- Dominique Devriese

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type converters and a g++ bug
by greg landrum Oct. 18, 2002

Oct. 18, 2002

[Redhat 8.0, g++ 3.2, python 2.2, boost 1.29.0] I'm in the process of trying to get my brain around the new type conversion system in BPLv2 (it's definitely a lot more complex than the one in v1) and I hit this little beauty. The attached code snippet causes g++ to seg fault most beautifully: ----------------- convert2.cpp: In function `PyObject* foof(int)': convert2.cpp:13: internal error: Segmentation fault Please submit a full bug report, with preprocessed source if appropriate. See <URL:http://bugzilla.redhat.com/bugzilla/> for instructions. ----------------- The bad actor appears to be to_python_value Before i worry about the fact that I'm killing the compiler, I wanted to check that I am doing something reasonable. This snippet is the core of an attempt I was making for a general purpose converter which takes std::vectors on the C++ side and returns them to python as tuples. In BPLv1, I used something like this: ----------------- template <typename T> PyObject* to_python(std::vector<T> p) { int l=p.end()-p.begin(); typename std::vector<T>::iterator i; int idx; PyObject *res=PyTuple_New(l); for(i=p.begin(),idx=0;i!=p.end();i++,idx++){ PyTuple_SetItem(res,idx,to_python(*i)); } // FIX: is this needed? Py_INCREF(res); return res; } ----------------- which, though not pretty, was perfectly functional. Is there a straightforward equivalent to this in BPLv2? Thanks, -greg

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MillerIndex example and other notes
by daniel Oct. 17, 2002

Oct. 17, 2002

hi, and first of all congratulations to v2 boost.python - i feel it much easier to find my way around than in the previous version, specially due to the enhanced docs. thank you. i would like to ask/comment some points i noticed when upgrading to v2 my first and certainly buggy version of a boosted c++ api: let me start with the MillerIndex example filed in examples/do_it_yourself_convts.cpp of v1. i guess this is very similar to the faq posted by ralf on c++ vs native python containers: according to that, converrting MillerIndex to native python list would go like this: /*************************************************************/ class MillerIndex { public: int v[3]; }; struct MillerIndex_to_python { static PyObject* convert(MillerIndex const& mi) { boost::python::tuple result = make_tuple(mi.v[0],mi.v[1],mi.v[2]); return incref(result.ptr()); } }; struct MillerIndex_from_python { MillerIndex_from_python() { boost::python::converter::registry ::push_back(&convertible,&construct, boost::python::type_id<MillerIndex>()); } static void* convertible(PyObject* obj_ptr) { if ( ! PySequence_Check(obj_ptr)) { return 0; } if ( PySequence_Length(obj_ptr) != 3) { return 0; } return obj_ptr; // if the input object is convertible } static void construct(PyObject* obj_ptr, boost::python::converter ::rvalue_from_python_stage1_data* data) { boost::python::tuple t = extract<boost::python::tuple>(obj_ptr); void* storage; storage = ((boost::python::converter ::rvalue_from_python_storage<FloatVector>*)data)->storage.bytes; new (storage) MillerIndex; data->convertible = storage; MillerIndex& result = *((MillerIndex*)storage); for(int i=0;i<3;++i) { result.v[i] = extract<int>(t[i]); //checking omitted } } }; /*************************************************************/ IMHO this is pretty long and a bit akward, at least the from_python part. is their a more easy way of doing this ? or is this usage of boost.python disencouraged ? ------ extract<>() and the object class seemed to me really nice, enhancing features. i think i misunderstood the tutorial when it talks about instantiating class_<T> objects, though. according to it, i thought it was necessary to write down the class_>T> "declaration" just as if you were exposing the class to python but finally calling the constructor (http://www.boost.org/libs/python/doc/tutorial/doc/derived_object_types.html) but if you already registered a certain class_<T> in the module, you can instantiate python-objects from c++ of that type just by writing: object(T()); (i tried to create an instance by "re-declaring" class_<T> in my code and i got a registration error at execution time, saying: python: libs/python/src/converter/registry.cpp:74: void boost::python::converter::registry::insert(PyObject*(*)(const void*), boost::python::type_info): Assertion `slot == 0' failed another thing which i have not really played much with is about the reference counting. as long as you stay in the upper levels, exporting classes with class_<T> and using object/tuple/list etc. this is perfectly hidden, very nice. but if you have to write these converter things by hand, i would like to know how to get them back into the "boost refernce counting". e.g. if i have: PyObject *obj = createObjectFromTheTimesWhereBoostWasNotBorn(); { return Py_BuildValue("iii", 1,2,3); } how could i incorporate this using boost::python::def() ? greetings, daniel -- Daniel Kottow daniel.kottow(a)ipk.fhg.de Security and Testing Technology http://vision.fhg.de/~daniel Production Technology Centre Pascalstr. 8 - 9 Fraunhofer-Institut IPK Berlin D - 10587 Berlin

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strange error
by Stefan Seefeld Oct. 17, 2002

Oct. 17, 2002

hi there, here is a (python) error I'v run across a couple of times without understanding what it represents / comes from: Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: __repr__ returned non-string (type str) It looks as if I called (implicitely at least) a string conversion function but the __repr__ function didn't return what it is supposed to: a string. The most puzzling is now that I have defined a wrapper for a C++ method 'void Foo::bar(...)', and this error is printed when a call to 'foo' returns. The internals of Foo::bar are not seen by python, and the return value is void, where does a string conversion attempt come into play here ? Thanks, Stefan PS: I even tried r = foo.bar() print type(r) and then the 'print type(r)' would raise the above error...

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supporting binary strings
by greg Landrum Oct. 16, 2002

Oct. 16, 2002

The default string conversion behavior of BPLv2 truncates strings containing nulls. BPLv1 did not do this (Python strings containing nulls were properly passed to the C++ layer). I've made two small mods to change the behavior back. A context diff for the changes is attached. I'm not super comfortable with the new type conversion system yet, so I'm not 100% sure that my change from char* to string in the PyString converter isn't going to break things in other peoples' code (though all the tests pass for me). -greg

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Building C/C++ extensions for Python
by David Abrahams Oct. 16, 2002

Oct. 16, 2002

Enthought and Boost Consulting are proud to announce "Building C/C++ extensions for Python," an intense 3 day course taught by David Beazley, David Abrahams, and Eric Jones, the lead authors of SWIG, Boost.Python, and Weave. This hands-on course is geared toward C/C++ programmers and teaches the start-to-finish process of exposing C/C++ libraries for use in Python. Students are sure to benefit from this opportunity to learn from three of the leading experts in the field. The class teaches the fundamentals of designing and building Python extensions and addresses the common problems that arise during the process. Boost.Python, SWIG, and Weave are central to the discussion, and each is covered in depth. Fundamental topics such as handling reference counts and building Python 2.2 style extension types by hand are also covered. Other topics discussed include Pyrex, distributing extensions using distutils, debugging extensions, and solving shared library issues. The course is divided equally between lectures and hands-on programming sessions. Users will need to bring either a Linux or a Windows NT/2000/XP, network enabled, laptop to the class with Python 2.2 and a C++ compiler installed for the programming sessions. More information about setup requirements is available at the website. Space is limited. Website: http://www.enthought.com/training/building_extensions.html Signup Information: Call (512) 536-1057 to reserve your place. Dates: December 9th, 10th, and 11th, 2002 (Monday through Wednesday) Instruction Hours: Instruction runs from 9am-9pm on the first two days (with breaks for lunch, dinner, and between sessions), and 9am-6pm on the final day of the class. Location: The Driskill Hotel www.driskillhotel.com 604 Brazos Street Austin, Texas The Driskill is conveniently located in the heart of downtown Austin. And, yes, it has high speed internet connections in the guest rooms. What's Included: 3 nights of lodging All meals and snacks Unlimited caffeinated drinks Class materials 3 days of instruction Cost: $2400.00 US. About the Authors: David Beazley David is an assistant professor in the Department of Computer Science at the University of Chicago. He has worked on Python extension building since 1996 and is the creator of SWIG (www.swig.org). He is also the author of the "Python Essential Reference." David holds a PhD in Computer Science from the University of Utah. David Abrahams David is a founding member and moderator of Boost (www.boost.org) and heads Boost Consulting, a company dedicated to providing professional support and development services for the Boost C++ libraries and associated tools. He has been an ANSI/ISO C++ committee member since 1996, when he contributed a theory, specification, and implementation of exception handling for the C++ standard library. In his 14-year career he has developed applications for the desktop and embedded devices in the fields of music software, speech recognition, and circuit simulation. David holds a BSE in Computer Science from the University of Pennsylvania. Eric Jones Eric has a broad background in engineering and software development and leads Enthought's product engineering and software design. Eric is a lead developer on the SciPy (www.scipy.org) and Weave projects and has taught numerous courses about Python and how to leverage it for scientific computing. Prior to co-founding Enthought, Eric worked in the fields of numerical electromagnetics and genetic optimization. Eric holds a PhD degree in Electrical Engineering from Duke University. -- David Abrahams dave(a)boost-consulting.com * http://www.boost-consulting.com Building C/C++ Extensions for Python: Dec 9-11, Austin, TX http://www.enthought.com/training/building_extensions.html

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