input: Write a function to generate a 7x7 grid where each cell contains either a '#' or a space character, based on whether the sum of its row and column indices is even or odd. If the sum is even, the cell should contain '#'; otherwise, it should contain a space. The function should return None, as the primary purpose is to print the grid directly to the console.
  assert generate_grid() is None
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()