Python Challenge - Unique Characters in a String

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def unique_characters(string_in):

  if string_in == "":
    return "Error"

  string_list = [i for i in string_in]
  dupes = filter(lambda x: string_list.count(x ) > 1, string_list)

  if list(dupes):
    return False
  else:
    return True

print(unique_characters("apple"))

(1) Turn the string into a list.
(2) “dupes” filters the list to only the characters that are duplicates… I like the filter function!
(3) If dupes is non-empty, return False, since there is at least one duplicate. If dupes is empty, return True, since there are no duplicates.