[Question] Why `.setdefault` in code example in README?

[weakish]

In README:

def get_top_songlist():
    # ...
    for data in datalist:
        music_info = {}
        music_info.setdefault("song_name", data.get("song_name"))
        music_info.setdefault("artist", data.get("artist"))
        music_info.setdefault("album_name", data.get("album_name"))
        # ...

music_info is (re)assigned to an empty dictionary on the start of every loop, so why

music_info.setdefault(k, v)

is used instead of directly

music_info[k] = v

?