input: 
  def print_checkerboard(size: int):
      """Prints a checkerboard pattern of the given size. 
      The pattern consists of `#` characters on black cells 
      and spaces on white cells. Black cells are determined 
      by the sum of their row and column indices being even.
  
      >>> print_checkerboard(7)
      # # # # #
       # # # # 
      # # # # #
       # # # # 
      # # # # #
       # # # # 
      # # # # #
      """
      for i in range(size):
          for j in range(size):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()
  
output:     for i in range(size):
          for j in range(size):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()