input: Write a function to generate a chessboard pattern of '#' and spaces by iterating through rows and columns where each character is printed based on whether the sum of its row and column indices is even or odd.
  assert chessboard_pattern()==None
output: def chessboard_pattern():
      for i in range(8):
          for j in range(8):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()