[C++-sig] BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS default args core dump

[Ralf W. Grosse-Kunstleve]

Hi Holger,

You don't need the BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS macro if you support keyword arguments (which is usually best). It should be as simple as:

.def("foo", &DefaultArgs::foo, (bp::arg("arg1")=100, bp::arg("arg2")=10))


The FUNCTION_OVERLOADS macros are more or less a relict. It is almost always best to follow the recipe above.

General remarks: use valgrind to find sources of segmentation faults and bus errors; look in boost/libs/python/test for role models to follow (everything you see in there is certain to work).


Ralf



>________________________________
>From: Holger Joukl <Holger.Joukl at LBBW.de>
>To: cplusplus-sig at python.org
>Sent: Monday, May 9, 2011 8:14 AM
>Subject: Re: [C++-sig] BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADSdefault args core dump
>
>
>Hi,
>
>this is basically a re-post of a problem I posted 5 weeks ago, on which
>there's
>been no echo whatsoever. Now, I'm unsure if this is because I posted on
>April 1st,
>nobody has ever seen this problem on his platform, nobody ever uses the
>BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS macro this way or I'm doing s.th.
>blatantly
>stupid.
>
>What nags me is that I don't think I'm doing something exotic and,
>moreover, that
>I see different behaviour depending on execution context, i.e. run in a
>script with
>or without previous method call(s) vs interactive interpreter session.
>
>I'll try to summarize the problem a bit more(see below for a link to the
>original post
>for reference):
>
>I'm having trouble wrapping a very simple member function with Boost.Python
>using the
>BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS macro, getting a segmentation fault
>(sometimes
>a bus error).
>
>I run into the problem both with Boost 1.44.0 and 1.46.1, running on
>Solaris 10/Sparc
>using gcc 4.5.1 and Python 2.7.1.
>
>I can reproducibly avoid the segfault and see an (expected) exception iff
>the code is
>* not run in an interactive interpreter session and
>* if there is a boost-induced exception succesfully raised before the
>critical call
>(which I don't understand at all).
>
>##### wrapped class
>// file default_arguments_class.hpp
>class DefaultArgs {
>public: // member functions
>    int foo(int arg1=100, int arg2=10) { return arg1 - arg2; };
>};
>
>##### wrapper code
>
>// file default_arguments_wrap.cpp
>
>#include <boost/python.hpp>
>#include "default_arguments_class.hpp"
>
>namespace bp = boost::python;
>
>BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(DefaultArgs_foo_overloads,
>DefaultArgs::foo, 0, 2)
>BOOST_PYTHON_MODULE(defaultargs)
>{
>    bp::class_<DefaultArgs>("DefaultArgs", "DefaultArgs class docstring")
>        .def("foo_macro_a2", &DefaultArgs::foo,
>DefaultArgs_foo_overloads((bp::arg("arg2"))))
>    ;
>};
>
>##### In use in interactive interpreter session:
>
>>>> import defaultargs
>>>> d = defaultargs.DefaultArgs()
>>>>
>>>> try:
>...     print "d.foo_macro_a2(1, 2, 3):", d.foo_macro_a2(1, 2, 3)
>... except Exception, e:
>...     print e
>...
>d.foo_macro_a2(1, 2, 3): Python argument types in
>    DefaultArgs.foo_macro_a2(DefaultArgs, int, int, int)
>did not match C++ signature:
>    foo_macro_a2(DefaultArgs {lvalue})
>    foo_macro_a2(DefaultArgs {lvalue}, int)
>    foo_macro_a2(DefaultArgs {lvalue}, int, int arg2)
>>>> print "d.foo_macro_a2(arg2=60):", d.foo_macro_a2(arg2=60)
>Bus Error (core dumped)
>
>##### In use within a script:
>$ cat foo.py
>import defaultargs
>d = defaultargs.DefaultArgs()
>
>try:
>    print "d.foo_macro_a2(1, 2, 3):", d.foo_macro_a2(1, 2, 3)
>except Exception, e:
>    print e
>
>print "d.foo_macro_a2(arg2=60):", d.foo_macro_a2(arg2=60)
>
>$
>PYTHONPATH=/var/tmp/boost_apps/boost/build/boost_1_46_1/py2.7/minimal/gcc-4.5.1
>/debug/ /apps/local/gcc/4.5.1/bin/python2.7 foo.py
>d.foo_macro_a2(1, 2, 3): Python argument types in
>    DefaultArgs.foo_macro_a2(DefaultArgs, int, int, int)
>did not match C++ signature:
>    foo_macro_a2(DefaultArgs {lvalue})
>    foo_macro_a2(DefaultArgs {lvalue}, int)
>    foo_macro_a2(DefaultArgs {lvalue}, int, int arg2)
>d.foo_macro_a2(arg2=60):
>Traceback (most recent call last):
>  File "/ae/data/tmp/hjoukl/foo.py", line 9, in <module>
>    print "d.foo_macro_a2(arg2=60):", d.foo_macro_a2(arg2=60)
>Boost.Python.ArgumentError: Python argument types in
>    DefaultArgs.foo_macro_a2(DefaultArgs)
>did not match C++ signature:
>    foo_macro_a2(DefaultArgs {lvalue})
>    foo_macro_a2(DefaultArgs {lvalue}, int)
>    foo_macro_a2(DefaultArgs {lvalue}, int, int arg2)
>
>My original post complete with bjam etc. can be found here:
>http://article.gmane.org/gmane.comp.python.c%2B%2B/15163
>
>Holger
>
>
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