input: 
  def print_checkerboard():
      """Prints a checkerboard pattern consisting of '#' and spaces, with a size of 7x7.
      >>> print_checkerboard()
      ## ## ##
       ## ## ##
      ## ## ##
       ## ## ##
      ## ## ##
       ## ## ##
      ## ## ##
      """
      for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()
  
output:     for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()