Yes, just tried it and it stops the ball…
But it works fine with the last correction I did (putting the “if” statement after the random command).
What is strange is this:
each “list” contains 21 sub-lists (2 dimensional array). When x or y gets at position 0 or 20, it then jumps to the opposite end (if 0 then it becomes 20, etc). Then the loop simply resumes and updates x and y from where it jumped. So the ball will “cross a border” and reappear at the opposite side, then just resume its motion inside borders and can even go all the way to the opposite side again. How can lists do that ?
But anyway I should not use long strings, that was just to have an empty background (DOS nostalgia…). I could do something simpler with 19 elements per list, but it will fill the background with symbols. That is also why I want to get to know at least one GUI framework for python, so I can test commands in a “live” environment (like a “window” to catch the mouse, for example).