Gotta Get Back To Hogwarts

After the war, most of the students go back to Hogwarts to finish there seventh year. The minister of magic, Kingsley Shacklebolt, has called a re-sorting of these returning 7th-year students. Almost everyone gets sorted into the house they had before. Except for one certain insufferable know it all.
How will the Headmaster and potions professor deal with his newly sorted snake?