matplotlib with X11

[Frank Schima]

>> 'GTKAgg' (gives 'ImportError: No module named _backend_gdk'),
>> and several others, with no success.
> 
> GTKAgg should display over X11, provided GTK is built against X11 and
> not Aqua. Can you file a ticket at trac.macports.org, and assign it to
> me (ram at macports.org), make sure to include a script that shows the
> problem.

Do you have py27-matplotlib installed with the +gtk2 variant?