input: Write a function to combine two strings and reverse the result in Python. The function should take two string inputs and return the reversed combined string. If either of the inputs is empty, the function should return the non-empty string reversed.
  assert combine_and_reverse("Hello ", "world!")=="!dlrow olleH"
  assert combine_and_reverse("hello", "")=="olleh"
  assert combine_and_reverse("", "Python")=="nohtyP"
  assert combine_and_reverse("", "")==""
  assert combine_and_reverse("Good ", "morning!")=="!gninrom dooG"
output: def combine_and_reverse(str1, str2):
      if not str1:
          return str2[::-1]
      elif not str2:
          return str1[::-1]
      else:
          return (str1 + str2)[::-1]