tkinter: using scrollbars on a canvas

I’m trying to make a canvas scrollable. However, once I try to set up scrollbars to work with the canvas, tkinter seems to completely ignore the dimensions I initially set for my canvas. I’ve tried packing them all in a frame, setting the canvas to fill the frame and then setting the frame size, but that presents the same problem unless I set the frame to fill the window as well, which isn’t what I want. Basically, I want a fixed-size canvas with scrollbars on it. My current code looks like this (in python 3.1):