def has_preview(song_data):
    """ 
    Returns True if a song's Spotify metadata contains a valid preview URL 
    Inputs:
        song_data : json/dict track metadata object from Spotify API
                    (ex: output of call to spotipy.track(track_id))
    Outputs:
        bool
    """
    preview = song_data['preview_url']
    if (type(preview)==str) and ('p.scdn.co' in preview):
        return True
    return False