Mailman 3 July 2003 - Cplusplus-sig

return_self_policy
by Nikolay Mladenov July 19, 2003

July 19, 2003

Posting return_self policy implementation Nikolay ''' >>> from return_self import * >>> l1=Label() >>> l1 is l1.label("bar") 1 >>> l1 is l1.label("bar").sensitive(0) 1 >>> l1.label("foo").sensitive(0) is l1.sensitive(1).label("bar") 1 ''' def run(args = None): import sys import doctest if args is not None: sys.argv = args return doctest.testmod(sys.modules.get(__name__)) if __name__ == '__main__': print "running..." import sys sys.exit(run()[0])

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def() vs. add_property()
by Stefan Seefeld July 18, 2003

July 18, 2003

hi there, I'v got a class that holds a reference to an external object, which is accessible through a simple method: class Origin {}; class Event { public: Event(const Origin *o) : my_origin(o) {} const Origin *GetOrigin() { return my_origin;} private: const Origin *my_origin; }; I can expose the 'Event' and 'Origin' classes, as well as &Event::GetOrigin, to python. However, I'd rather like to make the origin accessible as a (read-only) property. The problem is that the 'add_property' method doesn't take a return value policy, so I have no way of telling python how to wrap the pointer. What is the suggested way to do that ? Regards, Stefan

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plans for a bugfix release ?
by Dominique Devriese July 17, 2003

July 17, 2003

Hi, I'm the main developer of Kig [1]. I have just committed the code for python scripting to the CVS repository, but I'm receiving bug reports from people not able to compile the new code because of the small typename problem that was fixed in Boost.Python some time ago [2] ( the fix is in CVS, right ? ). Are there any plans to release a fixed version of Boost.Python any time soon, and what is the policy on Boost.Python releases in general ? thanks domi Footnotes: [1] http://edu.kde.org/kig [2] http://mail.python.org/pipermail/c++-sig/2003-May/003889.html and http://mail.python.org/pipermail/c++-sig/2003-May/003896.html

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global variable
by Stefan Fleiter July 16, 2003

July 16, 2003

Hi, I am using pyste of boost.python to wrap a library. This library has an init function 'init' which allocates an object and sets a global pointer 'ptr' to it. This function can only be called once, so 'ptr' can or should never be changed. 1. How can I access 'ptr' or '*ptr'? 2. I have a function returning this 'ptr', what is the right call-Policy? Many thanks, Stefan

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implicit_convertible extension
by Stefan Seefeld July 16, 2003

July 16, 2003

hi there, I'm browsing through the documentation as well as the mailing list archive to find the best way to convert between a C++ type (boost::posix_time::time_duration) and a python type (double). Conversion should happen implicitely, i.e. I have a bunch of functions taking a time_duration argument, which I want to be able to call in python passing simple doubles. Looking at the documentation for implicit_convertible, I find the requirements a bit restrictive. I think it may be convenient to be able to provide converter functions that do the conversion even if the two types themselfs are totally unaware of each other (i.e. no cast operators, no special constructors required). Then, instead of saying implicitly_convertible<X, double>(); implicitly_convertible<double, X>(); I would expect to say X double_to_X(double); double X_to_double(const X &); ... implicitly_convertible<X, double>(X_to_double); implicitly_convertible<double, X>(double_to_X); Does this make any sense ? Does something like this already exist ? Thanks, Stefan

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debug version of boost.python loads the wrong python dll
by Lutz Paelike July 16, 2003

July 16, 2003

Hi all, i have the following problem: I use boost.python 1.30.0 to embed python into my program. I use VC++ 6 on windows 2000. Works great if i build a Release version , but if i want to use a debug version my program crashes with the following error: Fatal Python error: Interpreter not initialized (version mismatch?) i tracked this down and noticed that during loading the wrong dll is loaded. it doesn't matter if debug version or not it always loads python22.dll instead of python22_d.dll for the debug version. i guess that's causing the problem, but how can i solve it ? cheers, lutz

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compile time error triggered by gcc's '-pedantic' flag
by Stefan Seefeld July 15, 2003

July 15, 2003

hi there, I'm compiling a python extension containing a method returning an internal pointer, so I use: namespace { class Foo {}; class Bar { public: Foo *foo() { return &my_foo;} private: Foo my_foo; }; } BOOST_PYTHON_MODULE(Sandbox) { python::class_<Foo, boost::noncopyable> foo("Foo", python::no_init); python::class_<Bar, boost::noncopyable> bar("Bar", python::no_init); bar.def("foo", &Bar::foo, python::return_internal_reference<>()); } Whenever I try to compile that with gcc -pedantic, I get an error which ends with the lines ... /usr/local/ORTHOsoft/include/boost/python/class.hpp:253: instantiated from `boost::python::class_<T, X1, X2, X3>& boost::python::class_<T, X1, X2, X3>::def(const char*, A1, const A2&) [with A1 = <unnamed>::Foo*(<unnamed>::Bar::*)(), A2 = boost::python::return_internal_reference<1, boost::python::default_call_policies>, T = <unnamed>::Bar, X1 = boost::noncopyable, X2 = boost::python::detail::not_specified, X3 = boost::python::detail::not_specified]' /homes/Developer/sseefel/error.cc:22: instantiated from here /usr/local/ORTHOsoft/include/boost/python/object/make_ptr_instance.hpp:37: invalid use of member `boost::mpl::bool_<false>::type' As a quick fix I'll just drop the '-pedantic' flag but I'm curious as to whether this is a problem with the boost::python code or with gcc. I'm using boost 1.30 and gcc 3.2, by the way. Thanks a lot, Stefan

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more problems with python::return_internal_reference<>
by Stefan Seefeld July 14, 2003

July 14, 2003

hi there, I'm compiling the following code with gcc 3.2: #include <boost/python.hpp> namespace python = boost::python; namespace { class Bar {}; Bar *BarFactory() { static Bar bar; return &bar; } } BOOST_PYTHON_MODULE(Sandbox) { python::class_<Foo, boost::noncopyable> foo("Foo", python::no_init); python::class_<Bar, boost::noncopyable> bar("Bar", python::no_init); bar.def("foo", &Bar::foo, python::return_internal_reference<>()); python::def("Bar", BarFactory, python::return_internal_reference<>()); //python::return_value_policy<python::manage_new_object>()); } That compiles fine, but when I call the 'Bar' constructor from python, I get >>> from Sandbox import * >>> bar = Bar() Traceback (most recent call last): File "<stdin>", line 1, in ? IndexError: tuple index out of range What is going on here ? What does the boost::python runtime do with the returned value that involves a tuple ? When I replace the 'return_internal_reference<>' policy by 'return_value_policy<manage_new_object>' the function call returns successfully. But of course, that would crash at the end of the application... Thanks again, Stefan

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boost::python docstrings
by Daniel Holth July 14, 2003

July 14, 2003

Hello. I'm working on a module that exposes xmms_remote_* to Python. It's mostly done and in pypi but I would like help(xmms) to be more informative. What's the best way to change jump_to_time(...) Seek to a number of milliseconds past the beginning of the current file. to jump_to_time(t) Seek ... file. ? Thanks, Daniel Holth http://dingoskidneys.com

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boost::python and threads
by Vladimir Vukicevic July 14, 2003

July 14, 2003

Howdy, I'm working on wrapping a C++ library that heavily uses threads internally, and makes callbacks to user-defined functions on various non-user-created threads. (This is basically the situation that provided the impetus for PEP 311, after discussion on python-dev -- note that I'm working with Python 2.3 because of this, but I beileve that the PEP 311 patch could be back-ported to 2.2 should anyone need it.) However, I'm running into problems getting the correct wrappers for my classes, to get the various Py_BEGIN_ALLOW_THREADS/Py_END_ALLOW_THREADS and PyGILState_Ensure/PyGILState_Release combos in the various places. A little background about my problem: from an IDL for a Foo interface, I generate two C++ classes, "Foo" and "FooProxy". Both of these are wrapped in smart pointers and are always passed as such in the C++ library, so we have FooHandle and FooProxyHandle. If Foo defines a "bar();" operation, then class Foo will have a "virtual void bar() = 0;", and I have to subclass and implement it, from python or C++. I have a wrapper class that does the call_method<>() dance; in this wrapper class, I also place PyGILState_Ensure/PyGILState_Release around the call_method<>() call. FooProxy is a remote object that I get as a result of calling various functions to get a proxy -- it has a "void bar();" (non-virtual) that I can call. However, because the call can be made synchronously, I need to wrap the call to bar() with Py_BEGIN_ALLOW_THREADS and Py_END_ALLOW_THREADS. It's this problem that I'm directly dealing with -- I can't figure out a way to wrap class FooProxy such that I can manage the current ThreadState and the GIL around them. I can create another wrapper class that does the right thing and calls FooProxy::bar(), but functions are returning a FooProxy (not mywrapper_for_FooProxy), and I already have a Handle<FooProxy> as a wrapper specified in the boost::python class_... so I end up with incorrect types half the time. However, an alternative solution that I was thinknig of is to bake the thread smarts directly into boost::python. It seems to me that call_method and similar should always be wrapped with a PyGILState_Ensure/PyGILState_Release. Also, an additional call policy could be added, something like "allow_threads", which would cause b::p to call Py_BEGIN_ALLOW_THREADS and Py_END_ALLOW_THREADS around the function invocation on C++. This seems like a much more generally useful solution than me trying to do the dance in wrapper classes. Is this the right way to go? If so, I'd appreciate any pointers on implementing a new call policy, especially if it's possible to both specify allow_threads and a return_value_policy. Thanks, - Vladimir

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