input: 
  def print_chessboard(n: int) -> None:
      """
      Print an n x n chessboard pattern using '#' and spaces.
      The pattern should have '#' where the sum of the row index and column index is even, and spaces otherwise.
      >>> print_chessboard(2)
      # 
       #
      >>> print_chessboard(3)
      # #
       # 
      # #
      """
      for i in range(n):
          for j in range(n):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()
  
output:     for i in range(n):
          for j in range(n):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()