unique_characters() function that determines if any given
string has all unique characters (i.e. no character in the string is duplicated). If the
string has all unique characters, the function should return
True. If the string does not have all unique characters, return
unique_characters("apple") should return
This challenge and variations of it were reported to have been asked at interviews with Google. If you’ve covered the material in Pass the Technical Interview with Python or an equivalent, you should be able to solve this challenge. If you have trouble, try refreshing your knowledge there first.
Note that if the function is called with an empty string (“”), the program should return an error message.