[Ns-bugs] [Bug 127] Add trace callback type information for Python bindings

[code@nsnam.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=127





--- Comment #6 from Tom Henderson <tomh at tomh.org>  2009-01-10 12:24:17 EDT ---
(In reply to comment #5)
> (In reply to comment #4)
> > (In reply to comment #3)
> > > This is still an issue AFAIK.  Not P1 because Python bindings will be merged
> > > after ns 3.1.
> > > 
> > 
> > Gustavo, can you clarify the status of this?  My understanding is that:
> > 
> > 1) if a callback is exported explicitly at the API, it is possible to register
> > a python method with it, thereby enabling people to write python code for ns-3

Is the above true?  Are there any examples of it presently?

> > 
> > 2) but due to this bug, we just can't hook them through the trace hooks
> > obtained through the trace path
> > 
> > If I am correct, are there any examples (even a small sample program for
> > samples/ directory) of how to do this?  Someone here at UW would like to try
> > writing some Python ns-3 code.
> > 
> 
> The problem is that 1) in Python we cannot introspect the signature of a
> "callable" (i.e. function or method, or class instance with a __call__ method),
> and 2) NS-3 also does not provide an API that says what is the expected
> callback type for a certain trace path, but it eventually checks in runtime
> whether supplied callbacks are of the correct type.  Although the
> Config::Connect API accepts a generic callback type (CallbackBase) as
> parameter, it later matches it against one of the concrete callback types
> (Callback<R,T1,T2,...>).  So the Python bindings have to supply a concrete
> callback wrapper based on a Python callable for which I cannot obtain signature
> information.
> 
> I can think of two possible and contrasting ways to move forward:
> 
>  1- Add a new NS-3 API to give back callback type(s) regarding trace path.  The
> Python bindings could work things out and the Python API would turn out to be
> simple:
> 
> 
>    def my_callback(packet):
>       print packet
> 
>    ns3.Config.Connect("/NodeList/*/....", my_callback)
> 

clearly that would be nicer on users but I don't know what is involved in
supporting that.


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