input: Write a function to generate a 7x7 grid where each element is either a '#' or a space character, determined by whether the sum of its row and column indices is even or odd. The function should print the grid row by row.
  
  assert generate_grid()
  assert generate_grid()
  assert generate_grid()
  assert generate_grid()
  assert generate_grid()
output: def generate_grid():
      for i in range(7):
          row = ''
          for j in range(7):
              if (i + j) % 2 == 0:
                  row += '#'
              else:
                  row += ' '
          print(row)