Mailman 3 August 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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double free segfaults
by Ellery Newcomer Sept. 1, 2013

Sept. 1, 2013

Hello all. I have been trying to wrap a third party C++ library with boost::python (first time using boost::python!), and on a very simple example I seem to be getting double free segfaults, so I am here soliciting advice. Does anything stand out? In gdb, I can't seem to catch it calling any particular destructor more than once. In pure c++, the class I am wrapping does not exhibit any such segfaults on simple usage, eg { CMOOSApp *app = new CMOOSApp(); delete app; } and other classes in the library do not exhibit such segfaults when I wrap them. c++: #include <boost/python.hpp> #include <MOOS/libMOOS/MOOSLib.h> using namespace boost::python; BOOST_PYTHON_MODULE(MOOSCore) { class_<CMOOSApp, boost::noncopyable>("MOOSApp"); } python: import MOOSCore thing = MOOSCore.MOOSApp() results: $ python test.py *** glibc detected *** python: double free or corruption (out): 0x0000000000f92b50 *** ======= Backtrace: ========= /lib64/libc.so.6[0x3b8a4760e6] /lib64/libc.so.6[0x3b8a478c13] /usr/lib64/libboost_python.so.5(_ZN5boost6python15instance_holder10deallocateEP7_objectPv+0x15)[0x7f15ee57a0b5] /usr/lib64/libboost_python.so.5(+0x2a394)[0x7f15ee57a394] /usr/lib64/libpython2.6.so.1.0[0x3b9de9a715] /usr/lib64/libpython2.6.so.1.0[0x3b9de78287] /usr/lib64/libpython2.6.so.1.0(PyDict_SetItem+0xa7)[0x3b9de7acf7] /usr/lib64/libpython2.6.so.1.0(_PyModule_Clear+0x16d)[0x3b9de7c66d] /usr/lib64/libpython2.6.so.1.0(PyImport_Cleanup+0x18f)[0x3b9dee987f] /usr/lib64/libpython2.6.so.1.0(Py_Finalize+0x11b)[0x3b9def28ab] /usr/lib64/libpython2.6.so.1.0(Py_Main+0x596)[0x3b9deff2d6] /lib64/libc.so.6(__libc_start_main+0xfd)[0x3b8a41ecdd] python[0x400649] the class CMOOSApp is defined here: https://oceanai.mit.edu/svn/moos-ivp-aro/releases/moos-ivp-13.5/MOOS_V10Bet… my complete code can be found here on the off chance someone wants to tinker with it: https://bitbucket.org/ariovistus/moos-python

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Segfault with keyword arguments and overloads.
by Alex Mohr Aug. 8, 2013

Aug. 8, 2013

I'm hitting a repeatable segfault trying to upgrade our boost version. I believe there may be a bug with overload resolution in the presence of keyword arguments. Here's a minimal example that crashes for me. // C++ #include <boost/python.hpp> static void f1(int a0, int a1) { } static void f2(int a0, int a1, int a2) { } BOOST_PYTHON_MODULE(kwargCrash) { boost::python::def("f", f1, (arg("a1")=2)); boost::python::def("f", f2, (arg("a2")=2)); } # Python import kwargCrash kwargCrash.f(0, a1=2) Version info: boost 1.51.0, Python 2.7.5, gcc 4.8.1. In the example we pass one positional argument and one keyword argument. This should fail to match the second overload (f2) since two positional arguments are required, and should match and invoke the first (f1). Instead, it segfaults. Here's my hypothesis as to what's happening from inspecting the boost.python code: In libs/python/src/object/function.cpp, function::call() (line 123) - We consider overloads in reverse reg order, so we try 'f2' first. - We pass the if on line 138, since n_actual is 2, f->m_nkeyword_values is 1, and min/max_arity==3. - The if on line 144 passes, since kwargs were supplied. - The fn has kwargs, so we take the 'else' on line 152. - We reach the 'build a new arg tuple...' else clause on line 167. - We make a tuple of size 3 and set the first element with the positional arg '0'. - Now we loop arg_pos = 1 to max_arity-1 (line 180). - Line 183, we set: kv = PyTuple_GET_ITEM(f->m_arg_names, arg_pos). - Line 189, we do: PyTuple_GET_ITEM(kv, 0). In this case, I believe kv is actually None, not a tuple, which gives us a bogus result, and I crash in the PyDict_GetItem call. Here's why I believe kv is actually None: In function.cpp again, function ctor (line 67) - Consider when an instance is created for 'f2'. - Line 72: keyword_offset gets set to 2 (max_arity = 3, num_keywords = 1). - m_arg_names is created with size 3 (max_arity) - Line 80: loop and set the first 2 elements (keyword_offset) to None. So the leading elements of the tuple get set to None, until we actually have keywords -- those elements get set to pairs of kwarg-name, kwarg-value. If my inspection is valid, then the indexing logic in function::call is busted. It assumes that it always gets a tuple of name/value for kv if it gets to line 189. But in this case it gets None since the argument at index 1 has no keyword. Does this sound plausible? I'm a bit surprised this was working for us previously, as the code looks like it hasn't really changed. Maybe we were getting lucky and Python changed in a way that breaks us? I.e. maybe PyTuple_GET_ITEM actually gave None if kv was None, and we never had None as a key in the passed keywords dict. Assuming my hypothesis is true, I'm not sure what the right fix here is off the top of my head. Naively it seems like checking for None in m_arg_names and rejecting the overload might work, but it feels like the right thing to do is to rework the logic used to decide whether or not a call has a satisfactory combination of positional and keyword args. Any thoughts appreciated. Alex

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Engineering Roles At a startup
by yoibr Aug. 3, 2013

Aug. 3, 2013

I am a freelance recruiter currently hiring Product Engineer,Dev-Ops engineer and Infrastructure engineer for a product startup backed by the same investors as Facebook, Google, Skype, Groupon. Location:Bangalore For more info visit:http://wehire4u.blogspot.in/

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Engineering Roles At a startup
by yoibr Aug. 3, 2013

Aug. 3, 2013

I am a freelance recruiter currently hiring Product Engineer,Dev-Ops engineer and Infrastructure engineer for a product startup backed by the same investors as Facebook, Google, Skype, Groupon. Location:Bangalore For more info visit:http://wehire4u.blogspot.in/

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