[pygame] Advice on turning sprite (newbie)

[AdamC <kabads@xxxxxxxxx>]

I'm learning pygame (also trying to teach my sons in the ins and outs
of python) and am trying to write a small simple game where a tank
moves around the screen on the user's press of the cursor keys. I've
managed to get this working without the tank turning and without using
an object oriented approach. However, I'm now trying to get my tank
working using the following tutorial [0]. My sprite appears on the
screen and the function move_me is called and changes the value of
draw_pos. However, the tank doesn't move.

You can see my code at [1]. You can see vec2d.py at [2]

Really I'm after how to use the vec2d.py to get my tank turning - I've
been sitting on this one and thinking about it in isolation (sons
aren't up to speed with this yet) for a while and would really
appreciate any advice.

I'll also appreciate any general pointers about bad code, bad style
and any tips of how to more efficiently write this code.

Thanks in advance
Adam

[0] http://eli.thegreenplace.net/2008/12/13/writing-a-game-in-python-with-pygame-part-i
[1] http://dpaste.com/112074/
[2] http://dpaste.com/112075/