Suppose I want a 5x5 grid size list.
So if we want to use loops, then we can do this in this way
board =  for i in range(0, 5): board.append(['O'] * 5) print board
And if we want to generate same list without using loops, then we can do it as follows
board = ([['O'] * 5]) * 5 print board
So, the question is, what’s the difference between the two results. I know the results would be same, but in Codecademy Editor, it says,
It looks like your board has 5 references to the same row! This will cause problems later on. Read the hint for more information and use a for loop to complete this lesson