Mailman 3 August 2016 - Cplusplus-sig

Embedding and extending an application with python in c++
by Wiskey 5 Alpha Aug. 25, 2016

Aug. 25, 2016

Hello, I am trying to extend a C++ application using python as a scripting language. What I would like to do is : * run the c++ application * have the application iterate through a directory of python files * each python file has access to variables/classes in the c++ application I have listed the test program here : http://stackoverflow.com/questions/39066307. I am getting a core dump when executing the test. Any help would be appreciated. - Tim

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Re: [C++-sig] Cplusplus-sig Digest, Vol 94, Issue 2
by foxtog＠gmail.com Aug. 8, 2016

Aug. 8, 2016

The problem doesn't have anything to do with boost.python. The thing is in initializing numpy API pointer specifically PyArray_API*. If you print this pointer before creating the array, it'll turn out to be null. If you move import_array function just before the array creation call, it should work. You can find more details here http://docs.scipy.org/doc/numpy/reference/c-api.array.html in Miscellaneous section at the bottom. Regards, Alexandra > 05 авг. 2016 г., в 20:00, cplusplus-sig-request(a)python.org написал(а): > > Send Cplusplus-sig mailing list submissions to > cplusplus-sig(a)python.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://mail.python.org/mailman/listinfo/cplusplus-sig > or, via email, send a message with subject or body 'help' to > cplusplus-sig-request(a)python.org > > You can reach the person managing the list at > cplusplus-sig-owner(a)python.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Cplusplus-sig digest..." > > > Today's Topics: > > 1. Segmentation Fault (core dumped) on Python 3.5.2 but not > Python 2.7.12 (Matthew Conte) > 2. Re: Segmentation Fault (core dumped) on Python 3.5.2 but not > Python 2.7.12 (Stefan Seefeld) > 3. Re: Segmentation Fault (core dumped) on Python 3.5.2 but not > Python 2.7.12 (Matthew Conte) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 4 Aug 2016 13:10:23 -0400 > From: Matthew Conte <matt.p.conte(a)gmail.com> > To: cplusplus-sig(a)python.org > Subject: [C++-sig] Segmentation Fault (core dumped) on Python 3.5.2 > but not Python 2.7.12 > Message-ID: > <CAFwmYYjxXXVQV=6Wv8x_q4Uc2GjogR1OR_JSURhP3kCMrEb-gQ(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > So I'm trying to create a boost python module that simply creates and > returns a numpy array, > but the function crashes (sometimes) and it doesn't ever seem to crash on > Python 2. > > Here's the source code I made: > > #include <boost/python.hpp> > #include <numpy/ndarrayobject.h> > > using namespace boost::python; > > object create_numpy_array() { > npy_intp dims = 1; > long* data = new long[1]; > data[0] = 1; > PyObject* obj = PyArray_SimpleNewFromData(1, &dims, PyArray_LONGLTR, data); > boost::python::handle<> handle(obj); > boost::python::numeric::array arr(handle); > return arr.copy(); > } > > BOOST_PYTHON_MODULE(create) { > import_array(); > numeric::array::set_module_and_type("numpy", "ndarray"); > def("numpy_array", &create_numpy_array); > } > > > using a simple python script to test: > > import create > print(create.numpy_array()) > > > The stack trace indicates that the crash occurs on a boost::python::handle > destructor trying to decrease the ref count of a PyObject with a ref count > of 0. > > I've tried this on both Windows 7 and Ubuntu 16.04 both 64-bit. > > Thank you. >

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Segmentation Fault (core dumped) on Python 3.5.2 but not Python 2.7.12
by Matthew Conte Aug. 4, 2016

Aug. 4, 2016

So I'm trying to create a boost python module that simply creates and returns a numpy array, but the function crashes (sometimes) and it doesn't ever seem to crash on Python 2. Here's the source code I made: #include <boost/python.hpp> #include <numpy/ndarrayobject.h> using namespace boost::python; object create_numpy_array() { npy_intp dims = 1; long* data = new long[1]; data[0] = 1; PyObject* obj = PyArray_SimpleNewFromData(1, &dims, PyArray_LONGLTR, data); boost::python::handle<> handle(obj); boost::python::numeric::array arr(handle); return arr.copy(); } BOOST_PYTHON_MODULE(create) { import_array(); numeric::array::set_module_and_type("numpy", "ndarray"); def("numpy_array", &create_numpy_array); } using a simple python script to test: import create print(create.numpy_array()) The stack trace indicates that the crash occurs on a boost::python::handle destructor trying to decrease the ref count of a PyObject with a ref count of 0. I've tried this on both Windows 7 and Ubuntu 16.04 both 64-bit. Thank you.

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Exporting a c++ buffer type.
by Vincent Vande Vyvre Aug. 3, 2016

Aug. 3, 2016

Hi, I'm porting a lib to Python-3. This code works with Python-2 ------------------------------------------------------ const std::string Image::getExifThumbnailData() { Exiv2::DataBuf buffer = _getExifThumbnail()->copy(); // Copy the data buffer in a string. // First allocate the memory for the whole string... std::string data = std::string(buffer.size_, ' '); // ... then fill it with the raw data. for(unsigned int i = 0; i < buffer.size_; ++i) { data[i] = buffer.pData_[i]; } return data; ----------------------------------------------------- The object Exiv2::DataBuf contain the pixel's values of an image [R,G,B,R,G,B,...] It is described here (1) With Python-3 I get this error: buf_ = self._metadata._image._getExifThumbnailData() TypeError: No to_python (by-value) converter found for C++ type: std::vector<char, std::allocator<char> > Then, I've made some tests with memoryView, like this: ----------------------------------------------------- boost::python::object Image::getExifThumbnailData() { Exiv2::DataBuf buffer = _getExifThumbnail()->copy(); Py_ssize_t size = buffer.size_; Py_buffer py_buffer; PyObject exporter; int res = PyBuffer_FillInfo(&py_buffer, &exporter, &buffer.pData_, size, true, PyBUF_CONTIG_RO); if (res == -1) { PyErr_Print(); exit(EXIT_FAILURE); } boost::python::object memoryView(boost::python::handle<> (PyMemoryView_FromMemory (&exporter, size, PyBUF_READ))); return memoryView; } ---------------------------------------------------- But that doesn't compile. src/exiv2wrapper.cpp: In member function ‘boost::python::api::object exiv2wrapper::Image::getExifThumbnailData()’: src/exiv2wrapper.cpp:504:65: error: cannot convert ‘PyObject* {aka _object*}’ to ‘char*’ for argument ‘1’ to ‘PyObject* PyMemoryView_FromMemory(char*, Py_ssize_t, int)’ (&exporter, size, PyBUF_READ))); (1) DataBuf: http://www.exiv2.org/doc/classExiv2_1_1DataBuf.html Regards, Vincent

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