input: def print_checkerboard_pattern():
      """Print a 7x7 checkerboard pattern where '#' represents black squares and
      spaces represent white squares. A black square is printed if the sum of the
      row and column indices is even.
      >>> print_checkerboard_pattern()
      # # # # # #
       # # # # # #
      # # # # # #
       # # # # # #
      # # # # # #
       # # # # # #
      # # # # # #
      """
  
output:     for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end=' ')
              else:
                  print(' ', end=' ')
          print()