Why do you have to loop it twice?
I just copied the answer from another topic because I wanted to move on but I don't understand.
2nd question; what does the word "numbers" link to then? to nothing?
n = [[1, 2, 3], [4, 5, 6, 7, 8, 9]] # Add your function here def flatten(lists): results =  for numbers in lists: for n in numbers: results.append(n) return results print flatten(n) print flatten(n)