Mailman 3 October 2011 - 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.

4 6

wrapped std::vector slice affecting items in a python list
by babak April 2, 2012

April 2, 2012

Hi, I've come across some unusual behaviour that I was hoping some one might be able to explain to me. In python I have a list and a wrapped std::vector<MyCustomType> (using the vector_indexing_suite) where the list contains the items in the vector. If I slice insert items into the vector then the items in the python list change. The attached example illustrates this. Is this behaviour expected ? I'm quite confused as to what's going on so any help clarifying this would be greatly appreciated. thanks, Babak http://boost.2283326.n4.nabble.com/file/n3738972/test.py test.py http://boost.2283326.n4.nabble.com/file/n3738972/source.cpp source.cpp -- View this message in context: http://boost.2283326.n4.nabble.com/wrapped-std-vector-slice-affecting-items… Sent from the Python - c++-sig mailing list archive at Nabble.com.

3 7

Is there any class member method number limit for boost.python?
by Grant Tang Oct. 29, 2011

Oct. 29, 2011

Hi, I have a class wrapped to Python which has 334 member .def(). After I added one more method, i.e. .def(), it shows segfault when I import this class it in Python. Strangely, this only happens on 64 bit CentOS 4.8 with gcc 3.4.6. It works fine with the 335th member method on 32 bit CentOS 4.8 with gcc 3.4.6. And also works fine with both 32 and 64 bit CentOS 5.6 with gcc 4.1.2. I can comment any one of member methods to make the number of methods <= 334 in my class to make it work on the 64 bit CentOS 4.8. It looks like there is such member method number limit on this 64 bit gcc3.4.6 platform. Please help. Grant

2 1

Memory corruption in exception translation on OS X 10.7
by Jakob van Santen Oct. 27, 2011

Oct. 27, 2011

Hi all, I've run across what I think is a strange memory corruption bug affecting C++/Python exception translation on OS X 10.7. A short program that reproduces the bug follows: #include <boost/python.hpp> static void throwme() { throw std::invalid_argument("Bork!"); } struct Bork { void throwy() { throwme(); } }; #ifdef BORKED BOOST_PYTHON_MODULE(borked) { boost::python::class_<Bork>("Bork") .def("throwy", &Bork::throwy) ; #else BOOST_PYTHON_MODULE(good) { #endif boost::python::def("throwy", &throwme); } When compiled without the call to class_<Bork>::def(), the exception is caught in handle_exception_impl() and presented to Python as ValueError, as expected: [jakob@i3-dhcp-172-16-55-176:tmp/pybork]$ python -c "import good; good.throwy()" Traceback (most recent call last): File "<string>", line 1, in <module> ValueError: Bork! When compiled with -DBORKED, however, I get a bad free() inside the std::logic_error destructor: [jakob@i3-dhcp-172-16-55-176:tmp/pybork]$ python -c "import borked; borked.throwy()" python(77633) malloc: *** error for object 0x7fec22c735a4: pointer being freed was not allocated *** set a breakpoint in malloc_error_break to debug I first encountered this bug in a private fork of 1.38, but I can reproduce it with a freshly build copy of 1.47. It occurs when building with both llvm-gcc and gcc-gcc, regardless of the optimization level. I built the two test libraries like so: g++ bork.cxx -g -bundle -flat_namespace -undefined dynamic_lookup -Iboost/include -I/System/Library/Frameworks/Python.framework/Headers/ -Lboost/lib -lboost_python -DBORKED -o borked.so g++ bork.cxx -g -bundle -flat_namespace -undefined dynamic_lookup -Iboost/include -I/System/Library/Frameworks/Python.framework/Headers/ -Lboost/lib -lboost_python -o good.so Can anyone reproduce this? Cheers, Jakob

2 1

failed to install boost.python on Lion
by Liguo Kong Oct. 26, 2011

Oct. 26, 2011

Hello, I am trying to install boost.python on Mac Lion OS. I used python 2.6 installed by default and built boost.build with *./bootstrap.sh --set-toolset=gcc *and then *./b2 install --prefix=~/workspace/boost_build*. The gcc version is "gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.15.00)". I followed the instructions http://www.boost.org/doc/libs/1_41_0/more/getting_started/unix-variants.htm… to install boost.python with bjam --build-dir=/Users/lkong/workspace/boost_python toolset=gcc --with-python stage It fails with the message: Component configuration: - chrono : not building - date_time : not building - exception : not building - filesystem : not building - graph : not building - graph_parallel : not building - iostreams : not building - math : not building - mpi : not building - program_options : not building - python : building - random : not building - regex : not building - serialization : not building - signals : not building - system : not building - test : not building - thread : not building - wave : not building ...patience... ...patience... ...found 1540 targets... ...updating 77 targets... common.mkdir stage common.mkdir stage/lib common.mkdir /Users/lkong/workspace/boost_python/boost common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2 common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1 common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/numeric.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/list.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/long.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/dict.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/tuple.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/str.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/slice.o common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/from_python.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/registry.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/type_id.o common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/enum.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/class.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/function.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/inheritance.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/life_support.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/pickle_support.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/errors.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/module.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/builtin_converters.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/arg_to_python_base.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/iterator.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/stl_iterator.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object_protocol.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object_operators.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/wrapper.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/import.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/exec.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/function_doc_signature.o gcc.link.dll /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/libboost_python.dylib *ld: unknown option: -R* collect2: ld returned 1 exit status "g++" -L"/System/Library/Frameworks/Python.framework/Versions/2.6/lib" -L"/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/config" -Wl,-R -Wl,"/System/Library/Frameworks/Python.framework/Versions/2.6/lib" -Wl,-R -Wl,"/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/config" -o "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/libboost_python.dylib" -Wl,-h -Wl,libboost_python.dylib -shared -Wl,--start-group "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/numeric.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/list.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/long.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/dict.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/tuple.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/str.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/slice.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/from_python.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/registry.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/type_id.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/enum.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/class.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/function.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/inheritance.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/life_support.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/pickle_support.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/errors.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/module.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/builtin_converters.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/converter/arg_to_python_base.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/iterator.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/stl_iterator.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object_protocol.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object_operators.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/wrapper.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/import.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/exec.o" "/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/object/function_doc_signature.o" -Wl,-Bstatic -Wl,-Bdynamic -lpython2.6 -Wl,--end-group ...failed gcc.link.dll /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi/libboost_python.dylib... ...skipped <pstage/lib>libboost_python.dylib for lack of <p/Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/threading-multi>libboost_python.dylib... common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/numeric.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/list.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/long.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/dict.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/tuple.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/str.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/slice.o common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/converter gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/converter/from_python.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/converter/registry.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/converter/type_id.o common.mkdir /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object/enum.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object/class.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object/function.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object/inheritance.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object/life_support.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object/pickle_support.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/errors.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/module.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/converter/builtin_converters.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/converter/arg_to_python_base.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object/iterator.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object/stl_iterator.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object_protocol.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object_operators.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/wrapper.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/import.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/exec.o gcc.compile.c++ /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/object/function_doc_signature.o gcc.archive /Users/lkong/workspace/boost_python/boost/bin.v2/libs/python/build/gcc-4.2.1/release/link-static/threading-multi/libboost_python.a common.copy stage/lib/libboost_python.a ...failed updating 1 target... ...skipped 1 target... ...updated 75 targets... The problem "*ld: unknown option: -R*" also appeared when I tried the quickstart example as in http://www.boost.org/doc/libs/1_47_0/libs/python/doc/building.html Any ideas how to solve the problem? Thanks a lot. Liguo

2 1

two pitfals when extending c++ classes from python
by Holger Brandsmeier Oct. 25, 2011

Oct. 25, 2011

Dear list, The boost_python Tutorial describes nicely and very brief how to subclass a boost::python exported class in python. I stumbeled over two pitfalls, which I did not expect by reading the tutorial. 1) When you put a wrapper class around a pure virtual class, you have to remove the "no_init" argument, e.g. for the example in the tutorial class_<BaseWrap, boost::noncopyable>("Base", no_init) is wrong, it should be class_<BaseWrap, boost::noncopyable>("Base") This is also what is shown in the tutorial, but it is not mentioned, that adding 'no_init' makes your wrapper unusable. If you don't override __init__ in your python class or if you call the super constructor in your overriden __init__, then you actually get an error when "no_init" is present: RuntimeError: This class cannot be instantiated from Python So, yes, you might argue that I should have been warned by this error. But unfortunately for me that error was misleading. Given this error I assumed that you didn't want me to call the super constructor in my __init__ if my super class is pure virtual (why not? pure virtual classes simply shouldn't have constructors). Then I spend a lot of time debugging, why I couldn't pass my class back to C++ any more until I found that the tutorial didn't have a "no_init" argument. 2) The method that I export as overridable in python takes on argument `node` of type `const parfem::Node&`. The class Node is a virtual class. If I simply pass `node` to python then I obtain the misleading message TypeError: No to_python (by-value) converter found for C++ type: parfem::Node This message actually doesn't mean that there is no such converter, there is certainly one present. This method probably has to do with the fact that Node is exported as "noncopyable" and "no_init". Admittedly the problem here is how to handle the lifetime of the object and after thinking about it I fully why boost::python has a problem here. My solution was then to pass a smart pointer instance. I just wanted to point out that the error message was very misleading here for me. -Holger -- Holger Brandsmeier, SAM, ETH Zürich http://www.sam.math.ethz.ch/people/bholger

2 1

Re: [C++-sig] Cannot build Boost.Python
by Ramesh Ramaiyer Oct. 21, 2011

Oct. 21, 2011

Hi David, I am running to the same issue. I am new to Python as well. Can you let me know how you solved your issue ? Thanks Ramesh

2 1

Inheritance problem
by Erik Türke Oct. 17, 2011

Oct. 17, 2011

Hi all, currently i am facing a problem regarding inheritance with boost::python Here is a simple code snippet: class Base { public: virtual void print() { std::cout << "hello" << std::endl; } }; class BaseWrapper : public Base, public wrapper<Base> { public: BaseWrapper( PyObject *p ) : self(p) {} BaseWrapper( PyObject *p, const Base &base) : Base(base), wrapper< Base >(), self(p) {} virtual void _print() { print(); } private: PyObject const *self; }; class Derived : public Base { public: Derived() {} Derived( PyObject *p ) : self(p){} private: PyObject const *self; }; BOOST_PYTHON_MODULE( my_module ) { class_<Base, BaseWrapper>( "Base", init<>() ) .def("printIt", &BaseWrapper::_print) ; class_<Derived, bases<Base> >( "Derived", init<>() ); } And in python i want to have the following reslut: >>import my_module >> derived = my_module.Derived() >> derived.printIt() Actually this should print "hello" but instead throws an error saying: derived.printIt() Boost.Python.ArgumentError: Python argument types in Base.printIt(Derived) did not match C++ signature: printIt(_Base {lvalue}) I tried a lot of modification but always getting this message. Does somebody of you know what i am missing? Thanks a lot in advance! Best regards! -- Erik Türke Department of Neurophysics Max-Planck-Institute for Human Cognitive and Brain Sciences Stephanstrasse 1A 04103 Leipzig Germany Tel: +49 341 99 40-2440 Email: tuerke(a)cbs.mpg.de www.cbs.mpg.de

2 4

Writing to numpy array: good practices?
by Jonas Einarsson Oct. 11, 2011

Oct. 11, 2011

Dear list, First, sorry if this is a double-post, I got confused with the subscription. Anyhow, I seek an opinion on good practice. I'd like to write simple programs that 1) (In Python) allocates numpy array, 2) (In C/C++) fills said numpy array with data. To this end I use Boost.Python to compile an extension module. I use the (possibly obsolete?) boost/python/numeric.hpp to allow passing an ndarray to my C-functions. Then I use the numpy C API directly to extract a pointer to the underlying data. This seemingly works very well, and I can check for correct dimensions and data types, etcetera. As documentation is scarce, I ask you if this is an acceptable procedure? Any pitfalls nearby? Sample code: C++ void fill_array(numeric::array& y) { const int ndims = 2; // Get pointer to np array PyArrayObject* a = (PyArrayObject*)PyArray_FROM_O(y.ptr()); if (a == NULL) { throw std::exception("Could not get NP array."); } if (a->descr->elsize != sizeof(double)) { throw std::exception("Must be double ndarray"); } if (a->nd != ndims) { throw std::exception("Wrong dimension on array."); } int rows = *(a->dimensions); int cols = *(a->dimensions+1); double* data = (double*)a->data; for (int i = 0; i < rows; i++) { for (int j = 0; j < cols; j++) { *(data + i*cols + j) = really_cool_function(i,j); } } } BOOST_PYTHON_MODULE(Practical01) { import_array(); boost::python::numeric::array::set_module_and_type("numpy", "ndarray"); def("fill_array",&fill_array); } And in python this could be used such as: import Practical01 import numpy import matplotlib.pyplot as plt import matplotlib.cm as colormaps import time w=500 h=500 large_array = numpy.ones( (h,w) ); t1 = time.time() Practical01.fill_array(large_array) t2 = time.time() print 'Horrible calculation took %0.3f ms' % ((t2-t1)*1000.0) plt.imshow(large_array,cmap=colormaps.gray) plt.show() Simplicity is a major factor for me. I don't want a complete wrapper for ndarrays, I just want to compute and shuffle data to Python for further processing. Letting Python handle allocation and garbage collection also seems like a good idea. Sincerely, Jonas Einarsson

2 1

Passing opaque pointers between modules
by Glenn Ramsey Oct. 7, 2011

Oct. 7, 2011

Is it possible to pass an opaque pointer from one bpl module to another? Following the documentation [1] I am able to successfully pass an opaque pointer from one function in a module to another function in that same module. Attempting to pass the opaque pointer to another module results in an error like this: Python argument types in Module1.SetOpaque(Class1, class opaque_ *) did not match C++ signature: SetOpaque(class Class2 {lvalue}, class opaque_ *) If I try the same using void * and relying on the built-in converters I get a similar failure: No registered converter was able to extract a C++ pointer to type void * from this Python object of type void * Is there a way to do this? Glenn [1] <http://www.boost.org/doc/libs/1_47_0/libs/python/doc/v2/return_opaque_point…>

1 1