Real-time plotting

Hello everyone! I'm seeking help with real-time plotting using Python and MatPlotLib. I've encoutered several problems so far:
1. There is no function to just add a point to the existing curve, so each time the data is updated all the curve has to be redrawn. This is not a clean solution for the real-time plotting.
2. I'm trying to use threads in Python in order to be able to get the data and draw the curve at the same time. Sometimes it's working, and sometimes the graphics rendering just hangs. Moreover, if I try to use the Timer class for the plotting thread, it is invoked only one time. I wonder, if my threads are stirring with a graphical library ones. If there is no special thread handling with Tk, I'll investigate my code again.
I'll appreciate any help.
Thank you.
P.S.: Sorry, forgot to put a title in the previous post.