Lengthy operations can't be interrupted in PythonTurtle, as of today. This proves to be a huge problem (which is also related to #24).

User interface becomes unresponsive

Especially with loops, and worse, nested loops, users are quickly tempted to use large numbers (for ranges), which creates an unlucky situation at best (when having to wait for a few minutes) or the need to kill the application, e.g., for nested loops (when an operation of O(n²) or more was triggered).

Expected behavior

It should be possible to interrupt the calculations (e.g. by pressing <Ctrl>+C and/or the <Esc> key).
It should be easy to interrupt the turtle and return to the interpreter prompt.