how to use x11 as backend for matplotlib on Mountain Lion of Mac OSX?

hi, every one:

I used to use TkAgg as backend on my macbook for matplotlib which was
installed from macports. for a while, the plot window was launched in X11. after a latest macports update, it stopped using x11 instead a standalone python window will be used now.

I was wondering if there is a way to instruct matplotlib to open plot window in x11? thanks!