input: Write a function that takes no input and prints a 7x7 grid where each character is determined by whether the sum of the row and column indices is even or odd. If it is even, the character should be '#', otherwise, it should be a space.
  
  
  def print_grid():
      for i in range(7):
          for j in range(7):
              if (i + j) % 2 == 0:
                  print('#', end='')
              else:
                  print(' ', end='')
          print()
  
  
  assert print_grid() is None
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()