input: Write a function to combine two strings and reverse the result in Python. The function should take two input strings, concatenate them, reverse the concatenated result, and return the reversed string.
  assert combine_and_reverse_strings("Hello ", "world!")=="!dlrow olleH"
  assert combine_and_reverse_strings("Python ", "Programming")=="gnimmargorP nohtyP"
  assert combine_and_reverse_strings("", "Empty")=="ytpmE"
  assert combine_and_reverse_strings("Test", "")=="tseT"
  assert combine_and_reverse_strings(" ", "Space")=="ecapS "
output: def combine_and_reverse_strings(str1, str2):
      return (str1 + str2)[::-1]