You don't need else-statement after the loop in that case.

this is a bad idea because as new languages are added to a kata, catering to each language's syntax peculiarities requires writing a bunch of if:language markdown blocks in the description, which quickly becomes unmaintainable. i rewrote the description so that it does not use the words true or false instead

In python translation, in the description of what should be returned, True and False should be capitalized, according to Python syntax.

Print the result of len({string}) for yourself and see what you get)
And, by the way, you don't need ternary operator there. You could just return comparison result