example doesn't work

Check your matplotlibrc to make sure you have a windowing

    > toolkit backend selected (TkAgg, GTKAgg, WXAgg, etc.) It
    > sounds like you might have the postscript backend or similar
    > selected.

If you build from source, and no GUI toolkits are detected at build
time, then eiterh Agg or PS will be selected as your default backend.
However, you should still see output when running in verbose-helpful.

I have never seen the kind of behavior you describe. Could you give
us a little more information (are you building from source, what
version, what backend do you have set, what is your python version)?