input: Write a function to sort a list of strings by their lengths in ascending order.
  assert ascending_sort(["apple", "cat", "banana", "dog"]) == ["cat", "dog", "apple", "banana"]
  assert ascending_sort(["a", "ab", "abc", "abcd"]) == ["a", "ab", "abc", "abcd"]
  assert ascending_sort(["longest", "short", "tiny", "medium"]) == ["tiny", "short", "medium", "longest"]
output: def ascending_sort(strings):
      return sorted(strings, key=len)