Function quick_enharmonics 

pub fn quick_enharmonics(
    name: &str,
    direction: Direction,
    double_accidentals: bool,
) -> Vec<String>

music21’s _quickEnharmonicString: the other spellings of a pitch name one way, each a diminished second from the last, until a letter comes round again or base 40 runs out of names. double_accidentals false leaves the double sharps and flats out.