input: def print_chessboard_pattern():
      """
      Produce a 7x7 grid where each cell contains either a '#' or a space character, 
      alternating in a chessboard pattern. The top-left corner should start with '#'.
      
      >>> print_chessboard_pattern()
      # # # # #
       # # # # 
      # # # # #
       # # # # 
      # # # # #
       # # # # 
      # # # # #
      """
output:     for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end=' ')
              else:
                  print(' ', end=' ')
          print()