input: Write a function to sort a list of strings based on their length. 
  assert sort_strings(["Hello","World!","Good","Morning"])==["Good","Hello","World!","Morning"]
  assert sort_strings(["Python","Code","Snippet"])==["Code","Python","Snippet"]
  assert sort_strings(["a","ab","abc"])==["a","ab","abc"]
  assert sort_strings([])==[]
  assert sort_strings(["One"])==["One"]
output: def sort_strings(lst):
      return sorted(lst, key=len)