python 调用未绑定的超类构造方法

class Bird:
    def __init__(self):
        self.hungry = True

    def eat(self):
        if self.hungry:
            print('Aaaaah')
            self.hungry = False
        else:
            print('No. thanks')


class SongBird(Bird):
    def __init__(self):
        Bird.__init__(self)
        self.sound = 'squawk'

    def sing(self):
        print(self.sound)


class SongBird(Bird):
    def __init__(self):
        super(SongBird, self).__init__()
        self.sound = 'squawk'

    def sing(self):
        print(self.sound)