input: Write a function to generate a checkered board pattern with a given size. The function should print a 7x7 grid where each cell is either a '#' or a space ' '. A cell contains '#' if the sum of its row index and column index is even, otherwise it contains a space.
  def generate_checkered_board():
      for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()
  assert generate_checkered_board()==None
output: def generate_checkered_board():
      for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()