Anyone who's written a fair share of Python can immediately see "len(set(l)) == len(l)" as "no duplicate elements", this is such a standard way to check for duplicates in Python that the chances are you've see this expression in this exact form dozens if not hundreds of times already.

Agreed with "l" identifier and docstring/comment. You'd probably write it like this if you want it to look nice:

    from typing import Iterable, Any
    
    def is_unique(elements: Iterable[Any]) -> bool:
        "Returns True if the argument has no duplicate elements."
        elements = list(elements)
        return len(elements) == len(set(elements))