def METHOD_NAME(artist):
    """Given an artist string, split the "main" artist from any artist
    on the right-hand side of a string like "feat". Return the main
    artist, which is always a string, and the featuring artist, which
    may be a string or None if none is present.
    """
    # split on the first "feat".
    regex = re.compile(plugins.feat_tokens(), re.IGNORECASE)
    parts = [s.strip() for s in regex.split(artist, 1)]
    if len(parts) == 1:
        return parts[0], None
    else:
        return tuple(parts)