input: Write a function to generate a 7x7 grid where each cell is filled with a '#' if the sum of its row and column indices is even, and a space ' ' otherwise. The function should simply print the grid to the console.
  assert generate_grid()
output: def generate_grid():
      for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()