[Ns-bugs] [Bug 155] "std::ostream & os" parameters not Python friendly

[bugzilla-daemon@nsnam-www.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=155





------- Comment #1 from mathieu.lacage at sophia.inria.fr  2008-03-30 12:29 -------
(In reply to comment #0)
> In the Python bindings I'm working on
> (http://code.nsnam.org/gjc/ns-3-pybindgen-notracing/), I am getting errors
> like:
> 
> /home/gjc/projects/ns-3/ns-3-pybindgen-notracing/build/debug/ns3/csma-helper.h:68:
> Warning: Parameter '::std::ostream & os' error (used in static void
> ns3::CsmaHelper::EnableAscii(std::ostream & os, uint32_t nodeid, uint32_t
> deviceid) [member function]): TypeLookupError('std::ostream &',)
> 
> So, std::ostream is not being wrapped, but the problem is that I am not
> comfortable wrapping ostream in any form.  The main problem is passing as
> reference and lack of reference counting.
> 
> Conceptually, I could create my own PyOStream C++ subclass of ostream, which
> would redirect writes to a python file-like object.  But passing as reference
> or pointer is dangerous because there is no guarantee that python object will
> be kept alive for long.  Python users should not have to worry about life cycle
> issues that much, and they are not used to it.
> 
> If these NS-3 APIs operated on a reference counted object instead (e.g.
> Ptr<OStream>) things would be vastly safer to Python bindings... this
> Ptr<OStream> could have "std::ostream& GetStdOStream ()" method.  That would be
> fine as long as the std::ostream object life cycle management responsibility
> shifts away from the Python bindings into the NS-3 core itself.

Adding such a Ptr<Ostream> class in the public API looks horribly painful from
c++ and would kill the whole purpose of these helper methods which is to make
life easy to c++ programmers, so, I would be really annoyed to have to do this.

It would be nice to find a good solution for python though: how does python
handle formatted io to stdout and files ? Can you point me to a not-too-painful
introduction ? How does boost::python handle this case ?


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