input: Write a function that prints a 7x7 grid where each cell contains a '#' if the sum of its row index and column index is even, and a space ' ' otherwise.
  
  def print_grid():
      for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()
  
  print_grid()
output: def print_grid():
      for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()