Mailman 3 June 2009 - Cplusplus-sig

boost::python embedding error - runtime - Mac OS X - 1.38
by Igor Karpov Oct. 1, 2014

Oct. 1, 2014

Hi, I am trying to run the following program: #include <iostream> #include <Python.h> #include <boost/python.hpp> using namespace boost::python; using namespace std; int main(int argc, char** argv) { { // Using Python/C Py_Initialize(); PyObject* main_module = PyImport_ImportModule("__main__"); PyObject* globals = PyEval_GetGlobals(); PyObject* locals = PyEval_GetLocals(); PyRun_SimpleString("print 'Hello World, from Python/C!'\n"); Py_Finalize(); } { // Using boost::python Py_Initialize(); object main_module = import("__main__"); object main_namespace = main_module.attr("__dict__"); try { object ignored = exec("print 'Hello World, from boost::python!'\n", main_namespace); Py_Finalize(); } catch (error_already_set const& e) { PyErr_Print(); return 1; } } return 0; } on Linux (both x86 and x86_64), with Ubuntu's default version of Boost (1.34.1) installed, I am able to do so as expected: $ ./embed Hello World, from Python/C! Hello World, from boost::python! on Mac OS X, I get a runtime error: $ ./embed Hello World, from Python/C! Bus Error Running with gdb, this is the stack trace: Hello World, from Python/C! Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000000 0x00000000 in ?? () (gdb) where #0 0x00000000 in ?? () #1 0x00bb618f in PyEval_GetGlobals () #2 0x00bce0dd in PyImport_Import () #3 0x00bce2b0 in PyImport_ImportModule () #4 0x008127d4 in boost::python::import (name=@0xbffff4a8) at libs/python/src/import.cpp:20 #5 0x00004446 in main (argc=1, argv=0xbffff510) at embed.cc:22 For this Mac, boost version is latest (1.38) and python version is: Python 2.5.4 (r254:67917, Dec 23 2008, 14:57:27) [GCC 4.0.1 (Apple Computer, Inc. build 5363)] on darwin Is this a bug? I attached the source and the cmake file I am using to build, for convenience. Thanks, --Igor.

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CMake and getting starting with boost.python
by Braddock Gaskill Aug. 5, 2011

Aug. 5, 2011

Yesterday I became a boost.python user, after years of heavy SWIG usage. I would have started using boost.python years ago except for the bjam learning curve. I spent hours TRYING on multiple occasions, but got lost every time trying to get the page one example to build with bjam. Here is how to build the "greet" example with a four line CMake file: cat >>CMakeLists.txt <<EOF LINK_LIBRARIES(boost_python) INCLUDE_DIRECTORIES("/usr/include/python2.5") LINK_DIRECTORIES("/usr/lib/python2.5") # Not needed? ADD_LIBRARY(hello SHARED hello.cpp) EOF You WILL have to `mv libhello.so hello.so` after building. Works for me under Ubuntu Linux 6.10 after apt-get install cmake python2.5-dev boost-python-dev cmake make mv libhello.so hello.so ipython In [1]: import hello In [2]: hello.greet() Out[2]: 'hello, world' Boost.Python has been a joy to learn and use since I got past bjam. I had a moderately large API wrapped in just my first couple hours of learning (less time than I spent messing with bjam). Any additional advice for using CMake to build boost.python? Braddock Gaskill

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How to import a boost::python dll in windows?
by ichijoji Aug. 5, 2011

Aug. 5, 2011

I'm trying to port some research code that uses boost::python to expose a library to python to windows, but I'm having trouble importing the dll into python. I'm compiling using msvc 2005 and using python 2.5, but when I try to import the module I get this: Traceback (most recent call last): File "main.py", line 1, in <module> import object File "c:\code\sge\code\scripts\object.py", line 1, in <module> import sge ImportError: No module named sge My module is named sge and I'm compiling to sge.dll. Is there some obvious reason why python wouldn't be able to find my dll? When I compile on linux into an so this code works fine. -- View this message in context: http://www.nabble.com/How-to-import-a-boost%3A%3Apython-dll-in-windows--tf3… Sent from the Python - c++-sig mailing list archive at Nabble.com.

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Getting object for PyObject (reference counting)
by Murray Cumming Feb. 11, 2010

Feb. 11, 2010

I can't find any definitive documentation that tells me how I should get a boost::python::object to wrap an existing PyObject*. I guess that there's a way to do it that uses an existing reference, and a way that takes an extra reference. -- murrayc(a)murrayc.com www.murrayc.com www.openismus.com

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Fw: g++ compiler limitations other than -ftemplate-depth-n and -DBOOST_PYTHON_MAX_ARITY ?
by Christopher A Mejia Sept. 20, 2009

Sept. 20, 2009

Stefan / cplusplus-sig, Based on Stefan's encouragement, I developed a minimal complete test case exhibiting this problem, contained in the attached files. The compilation command I used was: g++ -DBOOST_PYTHON_MAX_ARITY=40 -I/data/cmejia/install/boost_1_39_0 -I/data/include/python2.6 -c -o foo.o foo.cpp As I explained earlier in the first message of this thread, this fails to compile, but if I remove one double argument towards the end (i.e. edit out one line of foo.hpp and two lines of foo.cpp) it does compile successfully. I would appreciate any further insight into this problem, and hopefully we can use this test case to make Boost.Python an even better tool. Thanks in advance, --Chris P.S. Unfortunately, I was unable to include preprocessed source from "g++ ... -E foo.cpp" because the result was too large for the mailing list system. Christopher A Mejia wrote: > Stefan, > > Thanks for your response. The API that I am trying to wrap is the > Data Client Server portion of the U.S. Naval Research Labs' SIMDIS > Analysis & Display Tool (simdis.nrl.navy.mil). This is free software, > but does require registration and there is a human in the loop of the > approval process. Anyway, I don't feel comfortable redistributing the > software (or preprocessed details), but if you're really interested > you could obtain it directly yourself. Sorry, I'm not interested enough to register at this time. :-) I merely tried to be helpful in debugging the issue. > Apparently this API is a good test case for pushing some of the limits > of Boost.Python. Since you agree that this is probably a compiler > issue, it's unlikely that you or anyone else would be able to > reproduce the same errors anyway. The only compiler issue I mentioned was a misleading error message. I still believe the real issue might be inside boost.python (where some code may not support your high arity, and can't be configured with BOOST_PYTHON_MAX_ARITY), but I lack details to be able to confirm this. > I came up with a workaround, which is to wrap a version of the > function without the last three arguments, i.e. from Python I am OK > with always having those last three parameters set to their default > values. But if anyone has any other ideas to try, I'd like to hear them. It would really be best to construct the proverbial "minimal complete test case" that allows others to reproduce the issue. You may consider writing some stand-alone test using similar calls as in your code, which you then may freely send do this list, or file as an issue to the boost tracker. Regards, Stefan -- ...ich hab' noch einen Koffer in Berlin... _______________________________________________ Cplusplus-sig mailing list Cplusplus-sig(a)python.org http://mail.python.org/mailman/listinfo/cplusplus-sig The following line is added for your protection and will be used for analysis if this message is reported as spam: (Raytheon Analysis: IP=82.94.164.166; e-from=cplusplus-sig-bounces+camejia=raytheon.com(a)python.org; from=seefeld(a)sympatico.ca; date=Jun 8, 2009 2:39:33 PM; subject=Re: [C++-sig] g++ compiler limitations other than -ftemplate-depth-n and -DBOOST_PYTHON_MAX_ARITY ?)

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Pybindgen/pygccxml integration
by Ben Fitzpatrick Aug. 20, 2009

Aug. 20, 2009

Hi everyone, I'm just starting to check out pybindgen after the messages I've seen floating around on this mailing list, and I have a question about the pygccxml integration. I've made a pure-virtual class with a pointer return type, like so: class pure_virtual_class { virtual int get_value(int* value)=0; virtual int put_value(int value)=0; static pure_virtual_class* Create(); }; Normally I'd call add_function('get_value', retval(int), [param('int *', 'value', transfer_ownership=True)]) (I think) But since I'm scanning the headers with gccxml, I'm not sure how to tell it to transfer the ownership. Right now it's giving me a TypeConfigurationError during 'parse', which appears to be because it doesn't know how to deal with the ownership. I looked in the documentation and couldn't find anything referencing this, and none of the examples use gccxml. Any ideas? Thanks, Ben Fitzpatrick

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pybindgen: allow_subclassing option causing reference parameters to be copied?
by J. Michael Owen July 8, 2009

July 8, 2009

Hi again, I've run across another issue confusing me as I try to use pybindgen, in this case it's the treatment of reference parameters in virtual methods where you're allowing the class to be subclassed from python. It looks like the helper class that is generated is making copies of parameters that are being passed as references, which is not what we want. Take the following example C++ classes: class A { public: A(const int val): mVal(val) {} private: int mVal; A(); A(const A& rhs); A& operator=(const A& rhs); }; class B { public: B() {} virtual ~B() {} virtual void some_virtual_method(const A& a) const { std::cerr << &a << std::endl; } private: }; I'd like to be able to create subclasses of B from python, so I try wrapping these classes with the following pybindgen code: mod = Module("ref_param_example") mod.add_include('"classes.hh"') a = mod.add_class("A") b = mod.add_class("B", allow_subclassing=True) a.add_constructor([param("int", "val")]) b.add_constructor([]) b.add_method("some_virtual_method", None, [param("A&", "a")], is_const=True, is_virtual=True) The resulting generated code contains the following: void PyB__PythonHelper::some_virtual_method(A & a) const { PyGILState_STATE __py_gil_state; B *self_obj_before; PyObject *py_retval; PyA *py_A; __py_gil_state = (PyEval_ThreadsInitialized() ? PyGILState_Ensure() : (PyGILState_STATE) 0); if (!PyObject_HasAttrString(m_pyself, (char *) "_some_virtual_method")) { B::some_virtual_method(a); if (PyEval_ThreadsInitialized()) PyGILState_Release(__py_gil_state); return; } self_obj_before = reinterpret_cast< PyB* >(m_pyself)->obj; reinterpret_cast< PyB* >(m_pyself)->obj = const_cast< B* >((const B*) this); py_A = PyObject_New(PyA, &PyA_Type); py_A->obj = new A(a); .... As you can see, the last line quoted here is trying to make a copy of the instance "a" that was passed in. In this example this will not compile because the copy constructor for A is private. In general we don't want to make copies of reference parameters regardless of course. Am I once again missing something here? Is there some way I can declare that the passed parameters for "some_virtual_method" should really be treated as references and not copied? Thanks! Mike.

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Re: [C++-sig] Simple Boost.Python and NumPy example--help me make, it better!
by Garth Coghlan June 30, 2009

June 30, 2009

Hi Chris, Have you looked at the PyUblas <http://mathema.tician.de/software/pyublas> library? This provides a neat interface to C++ with Numpy arrays. On the C++ side you end up with a class that inherits from boost::ublas::matrix, which does no data copying, and which has a nice interface. You can get a pointer to the underlying data as well. You'd still need to wrap your original class, but those wrapper functions would be simpler. Let me know if you need help. Garth cplusplus-sig-request(a)python.org wrote: > From: "Christopher A Mejia" <camejia(a)raytheon.com> > > Hi, > > I've been trying to do something that is I would think is a very common > task: I'm trying to expose to Python a C++ class with a member function that > inputs an array of data. On the Python side, I would like to use NumPy to > store this array of data. I've spent many hours searching online for a > simple example, but haven't found one. > <snip>

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Re: [C++-sig] pybindgen: Why do wrapped C++ containers not look more like python containers?
by J. Michael Owen June 28, 2009

June 28, 2009

Hi Taner, Thanks for the suggestion! I actually was trying the same solution, except I wasn't sure how to handle the iterators. I'll try it out as you do in your example -- are you able to iterate over the vector in python the usual way? As in "for x in vec:"? Two curious things I noted about wrapping "std::vector" myself: 1. I can't seem to get indexing access to work, even though I wrap an indexing operation with the python name "__getitem__" 2. I also can't get python's len function to work, even if I provide "__len__" as follows: veci.add_method("size", "int", [], custom_name="__len__") Have you been able to make either of those methods work? Thanks! Mike. On Jun 4, 2009, at 11:42 PM, Taner Yildirim wrote: > Dear Mike, > > Concerning your question about add_method for stl_vector, I was able > to add > almost all standard methods of std_vector by simply wrapping the > std::vector without > even using the mod.add_container!! Since I am very new to pybindgen, > I am not sure if there is anything wrong with this approach but it > seems to work quite well. > Hopefully Gustava can comment on this more: > > > In summary, here’s how I get the std::vector<int> work in python > using pybindgen without add_container: > > >>>>>>>>> THIS is the header file: tst1.h <<<<<<<<< > > #include<vector> > #include <iostream> > typedef std::vector<int> VecI; > typedef std::vector<int>::iterator Iter_VecI; > #here you can do typdef for other types like double, string, etc > >>>>>>> END OF THE HEADER FILE <<<<<<<<<<<<<<<<<<<< > > > And here's the pybind-gen code to generate the wrapper.cpp > > >>>>>>>>>>>>>> wrap.py <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< > > import sys,pybindgen > from pybindgen import ReturnValue, Parameter, Module, Function, > FileCodeSink > > def my_module_gen(file_out): > mod=Module('tst1') > mod.add_include('"tst1.h"') > iter_veci=mod.add_class('Iter_VecI') > # > veci=mod.add_class('VecI') > veci.add_constructor([]) > > veci > .add_constructor > ([Parameter.new('int','size'),Parameter.new('int','val' )]) > veci.add_constructor([Parameter.new('VecI','vec_int')]) > veci.add_method('begin','Iter_VecI',[]) > veci.add_method('end','Iter_VecI',[]) > > veci > .add_constructor > ([Parameter > .new('Iter_VecI','begin'),Parameter.new('Iter_VecI','end')]) > veci.add_method('push_back','void', > [Parameter.new('int','value')]) > veci.add_method('size',ReturnValue.new('int'),[]) > veci.add_method('pop_back','void',[]) > veci.add_method('at',ReturnValue.new('int'), > [Parameter.new('int','index')]) > veci.add_method('front',ReturnValue.new('int'),[]) > veci.add_method('back',ReturnValue.new('int'),[]) > veci.add_method('clear','void',[]) > veci.add_method('empty',ReturnValue.new('bool'), > [],is_const=True) > veci.add_binary_comparison_operator('==') > mod.generate(file_out) > > my_module_gen(sys.stdout) > > >>>>>>>>>>> END OF THE WRAPPER CODE <<<<<<<<<<<<<<<<<<<<<<<<<<<<< > > Here’s a simple shell script to generate the code > (I generate pyd since I work in mingw envirentment): > > >>>>>>>>> simple shell script to generate the library <<<<<<<<< > rm tst1.pyd wrap.cpp > python wrap.py > wrap.cpp > g++ -c wrap.cpp -IC:/Python25/include > g++ -shared -o tst1.pyd wrap.o -LC:/Python25/libs -lpython25 > # > >>>>>>>>>>> end of the script <<<<<<<<<< > > Here’s the usage of the tst1.pyd in python: > > >>> from tst1 import * > >>> dir() > ['Iter_VecI', 'VecI', '__builtins__', '__doc__', '__name__'] > >>> a=VecI() # default constructor > >>> a.size() # check the size > 0 > >>> a.push_back(2) # add an entry > >>> a.size() > 1 > >>> a.at(0) # get the value at entry index 0 > 2 > >>> a.push_back(2) > >>> a.push_back(3) > >>> a.size() > 3 > >>> b=VecI(a.begin(),a.end()) #constructor using iterator > >>> b.size() > 3 > >>> a==b # check if they are the same > True > >>> b.push_back(1) > >>> b.size() > 4 > >>> a==b > False > >>> b.clear() > >>> b=VecI(4,10) # constructor for 4 entry with value of 10 > >>> > >>> c=VecI(a) #contructor from an other vector > >>> c==a > True > >>> c.pop_back() > >>> c==a > False > >>> a.empty() > False > >>> a.clear() > >>> a.empty() > True > >>> > >>>>>>>>>>> SOME COMMENTS <<<<<<<<<<<<<<<<<<<<<<<<< > > Needless to say, one can simple change the type “int” in the wrapper > code to double, float, etc and everything works for that type. > Ideally, I would like to have this sort of wrapper header file > included in pybindgen for a generic type TTTT and then we can simply > specify what type TTT we want (like TTT=[‘int’,’float’, ‘string’]) > and then pybindgen could just automatically generate the each > template with the requested type in the wrapper code!!! Anyway, this > would be my solution until the pybindgen container will have all the > standards methods implemented!!! > > QUESTION: In this approach, Is it possible to add a custom > constructor (in the python end) > such as a=VecI([a python list of integer])??? And how do I get a > python list from my VecI object using list?? > I guess implementing these two things are not easy and probably > that’s why we have the > pybindgen-container module at first place!!! > > Anyway, hope what I wrote above is not a total non-sense (which is > quite possible considering I have only a week experience wit > pybindgen!!!). > > Best regards > Taner > > ******************************************************************************** > Dr. Taner Yildirim, Ph.D. Physicist, > Adjunct Associate Professor, > Materials Science and Engineering, > University of Pennsylvania > and > Computational and Neutron Science Team Leader, > NIST Center for Neutron Research, > National Institute of Standards and Technology, > 100 Bureau Drive, Gaithersburg, MD 20899-6100. > Email: taner(a)nist.gov or taner(a)seas.upenn.edu > PHONE: 301-975-6228 FAX : 301-921-9847 > Web : http:// webster.ncnr.nist.gov/staff/taner > ******************************************************************************** >

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Simple Boost.Python and NumPy example--help me make it better!
by Christopher A Mejia June 26, 2009

June 26, 2009

Hi, I've been trying to do something that is I would think is a very common task: I'm trying to expose to Python a C++ class with a member function that inputs an array of data. On the Python side, I would like to use NumPy to store this array of data. I've spent many hours searching online for a simple example, but haven't found one. So, I've finally gotten my own simple example working, but I'm not sure I'm handling everything correctly, and I'm sure there's room for improvement...so, I'm posting my example here in the hopes that this group can help me make it better. My goal here is to have short and simple code, at the expense of performance. For example, I'm willing to explicitly copy my data array, if that's what I need to do to make use of existing libraries. The files array_test.hpp and array_test.cpp below contain the class I would like to expose to Python. Note that the member function sum() expects a pointer to a double array and an integer for the lengh of the array. The files array_test2.hpp and array_test2.cpp contain a derived class which inputs a boost::python::numeric::array. The file array_test_ext.cpp uses Boost.Python to expose these classes to Python. Everything appears to be working (the final file array_test.py gives the answer I expect) but I still think there's room for improvement. Here are some questions I have: 1. Is it necessary for me to define a whole new derived class just to add the extra layer on top of the sum() member function? I'm guessing that adding another layer on top of an existing member function must be a pretty common usage pattern so I'm wondering if there's a cleaner way to do it. 2. What is the best way (and the correct syntax) to pass the boost::python::numeric::array into the member function? Right now, I'm just using the syntax for a simple pass-by-value, but maybe I should use pass-by-reference? And should I put a "const" somewhere? 3. I don't think it should be necessary to pass the length of the data array into my function. The boost::python::numeric::array class has an nelements() member function. When I use the nelements() member function, my code compiles, but I get a Python runtime error that NumPy ndarrays don't have an nelements() attribute. What is the correct way to extract the length of the data array from the NumPy array? 4. I must admit that I don't understand <extract>. Is there a more efficient way to copy the data from my Python NumPy array into the C++ double * array? Any answers or suggestions for improvement would be most welcome! --Chris // array_test.hpp #ifndef _ARRAY_TEST #define _ARRAY_TEST class array_test { public: double mysqr(double x); double sum(double *x, int n); }; #endif // array_test.cpp #include "array_test.hpp" double array_test::mysqr(double x) { return(x * x); } double array_test::sum(double *x, int n) { double thesum = 0.; for(int i = 0; i < n; i++) { thesum += x[i]; } return(thesum); } // array_test2.hpp #include <boost/python/list.hpp> #include <boost/python/numeric.hpp> #include "array_test.hpp" class array_test2 : public array_test { public: double sum(boost::python::list o); double sum(boost::python::numeric::array y, int n); }; // array_test2.cpp #include <boost/python/extract.hpp> #include "array_test2.hpp" double array_test2::sum(boost::python::list o) { std::size_t n = len(o); double *tmp = new double[n]; for(unsigned int i = 0; i < n; i++) { tmp[i] = boost::python::extract<double>(o[i]); } double thesum = array_test::sum(tmp, n); delete tmp; return(thesum); } double array_test2::sum(boost::python::numeric::array y, int n) { double *tmp = new double[n]; for(int i = 0; i < n; i++) { tmp[i] = boost::python::extract<double>(y[i]); } double thesum = array_test::sum(tmp, n); delete tmp; return(thesum); } // array_test_ext.cpp // This file has been generated by Py++. (and then edited...) #include "boost/python.hpp" #include "/home/cmejia/Python/boost/array_test.hpp" #include "/home/cmejia/Python/boost/array_test2.hpp" namespace bp = boost::python; BOOST_PYTHON_MODULE(array_test_ext){ bp::numeric::array::set_module_and_type("numpy", "ndarray"); bp::class_< array_test >( "array_test" ) .def( "mysqr" , (double ( ::array_test::* )( double ) )( &::array_test::mysqr ) , ( bp::arg("x") ) ) .def( "sum" , (double ( ::array_test::* )( double *,int ) )( &::array_test::sum ) , ( bp::arg("x"), bp::arg("n") ) ); bp::class_< array_test2, bp::bases< array_test > >( "array_test2" ) .def( "sum" , (double ( ::array_test2::* )( bp::list ) )( &::array_test2::sum ) , ( bp::arg("o") ) ) .def( "sum" , (double ( ::array_test2::* )( bp::numeric::array,int ) )( &::array_test2::sum ) , ( bp::arg("y"), bp::arg("n") ) ); }

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