def make_album(artist, title, num_songs=0):
    """Build a dictionary containing information about an album."""
    album_dict = {
        'artist': artist.title(),
        'title': title.title(),
        }
    if num_songs:
        album_dict['num_songs'] = num_songs
    return album_dict

album = make_album('metallica', 'ride the lightning')
print(album)

album = make_album('beethoven', 'ninth symphony')
print(album)

album = make_album('willie nelson', 'red-headed stranger')
print(album)

album = make_album('iron maiden', 'piece of mind', num_songs=8)
print(album)