Finally i found time and energy to write a new wiki page for ThePythonGameBook: http://thepythongamebook.com/en:part2:pygame:step020 : “How to shooting bullets from the end of a cannon barrel” Special thanks to Jonathan Persson for writing me an email about this problem. His email motivated me to wake up from winter sleep. Still a lot of existing wiki pages need improvement.
The code example is not a complete game but a working demo of a tank who can rotate, move, rotate it's turrent and fire tracer rounds and bullets. The rounds are always created at the correct position (muzzle) , including the rotation of tank and turret.
Also i finally got The Ubuntu Video editor up and running, allowing me to show a video of how the tankdemo looks like: