unique_chars = [char for char, count in counter.items() if count == 1] unique_chars.sort(reverse=True) return ''.join(unique_chars)

This code takes a dictionary "counter" as input, where the keys are characters and the values are the number of times each character appears in a string.

The code creates a list "unique_chars" that contains only the characters that appear once in the string (i.e. have a count of 1 in the dictionary).

The list is then sorted in reverse order (from highest to lowest ASCII value) using the "sort" method.

Finally, the sorted list is joined into a string using the "join" method and returned.

Overall, this code returns a string containing all the unique characters in the input string, sorted in reverse order.