title: Create and initialize 5x5 grid for Battleships
body: <p>So I just completed a section of CodeAcademy Battleship problem, and have submitted a correct answer but am having trouble understanding why it is correct.</p>
  
  <p>The idea is to build a 5x5 grid as a board, filled with "O's". The correct code I used was:</p>
  
  <pre><code>board = []
  board_size=5
  
  for i in range(board_size):
  
      board.append(["O"] *5)
  </code></pre>
  
  <p>However I'm confused as to why this didn't create 25 "O's" in one single row as I never specified to iterate to a separate row. I tried</p>
  
  <pre><code>for i in range(board_size):
  
      board[i].append(["O"] *5)
  </code></pre>
  
  <p>but this gave me the error: <code>IndexError: list index out of range</code>. Can anyone explain why the first one is correct and not the second one?</p>