Mailman 3 June 2013 - 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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sendkeys method
by sam Sept. 30, 2013

Sept. 30, 2013

Hello, Is there away(method) in C/C++ programming that make the software think that someone pressed the OK button, similar to sendkeys in VBS (WshShell.SendKeys ("{Enter}")) Thank you, Sam

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return boost::shared_ptr<some internal>
by Neal Becker June 14, 2013

June 14, 2013

I have a class that has a member something like this: class A { boost::shared_ptr<B> b; }; boost::shared_ptr<B> get_b (A const& ...) { return A.b; } where class B is already exposed to python in a different module. I tried to provide access to the internal member A.b: class_<A> ... .add_property ("b", &A::get_b) It seems that attempting to provide access to this internal member fails, with a message about no conversion from c++ type blah blah. The c++ type represented by this internal state is already exposed in a different python module, which has also been imported into python. >From what I can gather from ancient messages on the web, this usage just isn't going to work. Any thoughts?

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How can I have a global C/C++ variable that is shared between Python C/C++ extensions?
by octalber fest June 13, 2013

June 13, 2013

Dear list, Apologies if this question is slightly off-topic, but I thought I might get answers here rather than the other Python mailing lists. I have a rather specific issue with creating a Python C++ extension that I'm really stuck on it. These are the details... -- I have written a Python package almost completely in C++. The reason for doing so is because I want to manually wrap an existing C++ library, but that is irrelevant here. This Python package consists of a number of different extension modules, all of which I compile with distutils in a 'setup.py' script. These extension modules can be interrelated, in which case I link them by passing the shared library to the Extension constructor. To be clear, suppose I have two Python C++ modules, A and B, where B uses functions defined in A. These normally compile into A.so and B.so. Since B uses functions defined in A, I compile the A module as usual then I pass ':A.so' as a library to the libraries keyword in the Extension constructor for the B module. (The ':' lets g++ deal with the fact that the library does not start with the usual 'lib' prefix.) This works fine for linking functions and classes. My problem is as follows: I have defined some extern global C++ variables in A. While doing what I have described allows B to access functions in A, it actually seems to create a COPY of any global data defined in A. This is a real problem for me. It seems to me that the issue is essentially similar to having global variables across shared libraries. The solutions to this that I have found online do not seem to solve the problem. Any help would be so very appreciated!

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Alternate locations for BOOST_PYTHON_MODULE
by Trevor Haba June 12, 2013

June 12, 2013

Hello, I am attempting to make a large pre-existing code base accessible to python, so that I can run quick scripts to automate the behavior of certain classes for testing purposes. We are using C++ and python 3.3 with the boost.python library. I have a script to automatically generate the BOOST_PYTHON_MODULE( ... ) wrapper definitions for the C++ source code. But, because this is a pre-existing code base with other people already working on it, I would prefer to not have to modify the source code files of all of the classes by inserting the python wrappers at the bottom. All the examples I've seen show the BOOST_PYTHON_MODULE at the bottom of the C++ source file. Is it possible to put the BOOST_PYTHON_MODULE in a separate file, and #include the class it is wrapping? If so, how would I do this? And how would I configure the Jamroot file to compile these properly? Also, I'm targeting windows systems and using Visual Studio 2010, if that matters Thanks very much, Trevor

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Handling multiple GIL accesses
by Adam Preble June 9, 2013

June 9, 2013

Here's the double lock I'm afraid of: 1. Embedding program invokes some Python code with its embedded interpreter 2. The embedded interpreter, through running that code, ends up executing some code actually in the embedded program's environment. 3. This code back in the embedded program has another thread (here we go) that calls to some interfaces, of which one is written in Python. 4. The wrapper needs to acquire the GIL since it's going back into Python, and it's going into it from another thread entirely. At #4 right there I thought it was tricky when trying to do this. I guess the important thing to do is to make sure to store a unique state from each call to PyGILState_Ensure and to keep those in order when using PyGILState_Release. I think when I originally did this, I had a global pointer, which was bad news. I wanted to make sure I understand how to handle a particularly disruptive situation when embedding Python in another language. I've been following this with embedding Python in C++, and I also looked at this with embedding CPython in C# using Python.NET. The Python.NET library looks like it's surviving without double locking. Looking at its implementation, I wanted to review for posterity's sake how this is supposed to work. I know when I was first trying to do this in C++, I didn't really pull it off, and I wanted the next poor fool that's Googling for this to have a good shot at it. So do I have it?

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Inner class name
by John Reid June 4, 2013

June 4, 2013

Inner classes seem to be given the wrong name or perhaps this is by design. Could someone enlighten me? If I do: namespace py = boost::python; py::class_< T > outer( "Outer" ); py::scope( outer ); py::class_< U > inner( "Inner" ); then in python: import module as M print M.Outer.Inner gives "M.Inner" which doesn't exist. I'm not sure it is important, it just seems curious. John.

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Heap error with pyqt code embedded using boost python
by Sebastian Herbord June 3, 2013

June 3, 2013

Hi, hope this is an adequate mailing list for this quesion, appologies in advance if not. I'm trying to embed python into a C++/Qt application using boost python. This works pretty well except the whole program crashes when a pyqt slot is invoked that takes a QString as its parameter. This is a minimal example: #include <QCoreApplication> #include <boost/python.hpp> using namespace boost::python; bool handled_exec_file(str filename, object globals) { return handle_exception(boost::bind(exec_file, filename, globals, object())); } int main() { QCoreApplication a(argc, argv); Py_Initialize(); object main_module = import("__main__"); object main_namespace = main_module.attr("__dict__"); if (handled_exec_file("test.py", main_namespace)) { if (PyErr_Occurred()) { PyErr_Print(); } else { qCritical("unknown error in python code"); } } return a.exec(); } ------------------------- from PyQt4 import QtGui def editBoxChanged(text): pass app = QtGui.QApplication([]) widget = QtGui.QWidget() editBox = QtGui.QLineEdit(widget) editBox.textEdited.connect(editBoxChanged) # mark widget.show() app.exec_() This crashes the second I enter something in the line-edit (exception code c0000005). If I run this in a debugger I get "Invalid address specified to RtlFreeHeap( 00BD0000, 00CF8798 ) (1684.1f88): WOW64 breakpoint - code 4000001f (first chance)" instead every time I input a character. The crash doesn't happen if the marked python line is removed. Does anyone have an idea what might be causing this or how to further debug the issue? I'd appreciate any help. Sebastian

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Re: [C++-sig] Handling a custom C++ exception from Python
by Alex Leach June 2, 2013

June 2, 2013

On Sun, 02 Jun 2013 21:04:51 +0100, Александров Петр <petr_aleksandrov(a)mail.ru> wrote: > 02.06.2013 13:14, Alex Leach пишет: >> 1. Boost Python has a dedicated exception handling API[1] that >> doesn't require you to wrap the exception in a class_<> template. The >> class_ template is a bit heavy duty for registering exceptions, I >> think. Instead, I register exceptions like this:- >> >> #include <boost/python/exception_translator.hpp> >> >> void TranslateMyException(const MyException& err) >> { >> PyErr_SetString(PyExc_Exception, err.ptr()); >> } >> >> void RegisterMyExceptionTranslator(void) >> { >> boost::python::register_exception_translator< >> MyException&>( TranslateMyException ); >> } > I want to pass some info (it is numbers) from C++ to Python with the > exception. This info is stored in C++ exception object fields. Using > class_ I allow accessing these fields from Python. Well, that is one way to do it. Above, in TranslateMyException, you can do whatever you like with the C++ exception, though. I've been doing it that way,usually just creating a human-readable message from the C++ exception, then using the above mechanisms to set the exception for Python. To give your exception extra Python attributes, you might consider using the raw Python C API function, PyErr_NewException[1]. Your call, though. Cheers, Alex [1]: http://docs.python.org/2/c-api/exceptions.html#PyErr_NewException

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Handling a custom C++ exception from Python
by Александров Петр June 2, 2013

June 2, 2013

I want to catch a custom C++ exception in Python. I have described my custom exception class as usual: class_<CMyException>(...); and created a translator: void translate(CMyException const &e) { object o(e); PyErr_SetObject(PyExc_Exception, o.ptr()); } This exception can be caught from Python: try: do_something() except Exception as exc: #exc.args[0] - the custom exception object print exc.args[0] Is it safe to do in such a way? Is the Python object, created in the function "translate", destroyed? Need I add "Py_INCREF" to this function?

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