问一个关于super函数的问题

streethacker

我用如下这段代码调用父类SGMLParser的reset方法，可是初始化时就报错了。查了super的文档，对它的几种调用形式没怎么理解。请各位指教，谢谢
>>> class URLLister(SGMLParser):
        def reset(self):
                super(URLLister, self).reset()
                self.urls = []

       
>>> parser = URLLister()

Traceback (most recent call last):
  File "<pyshell#52>", line 1, in <module>
    parser = URLLister()
  File "G:\Python 2.7.2\lib\sgmllib.py", line 69, in __init__
    self.reset()
  File "<pyshell#51>", line 3, in reset
    super(URLLister, self).reset()
TypeError: must be type, not classobj

sunny7476

SGMLParser应该是一个旧式的类，不是新式的类。

streethacker

回复 2# sunny7476
嗯。是的。后来我也意识到了这一点，写了一些简单的类验证了一下，的确如此：

#旧式类不能使用super
>>> class OldStyle:
        def display(self):
                print "This is the old-style base class"

               
>>> class Extend(OldStyle):
        def display(self):
                super(Extend, self).display()
                print "This is the subclass of the OldStyle"

               
>>> old = Extend()
>>> old.display()

Traceback (most recent call last):
  File "<pyshell#11>", line 1, in <module>
    old.display()
  File "<pyshell#9>", line 3, in display
    super(Extend, self).display()
TypeError: must be type, not classobj


#新式类可以使用super
>>> __metaclass__ = type
>>> class NewStyle:
        def display(self):
                print "This is the new-style base class"

               
>>> class Extend(NewStyle):
        def display(self):
                super(Extend, self).display()
                print "This is the subclass of the NewStyle"

               
>>> ex = Extend()
>>> ex.display()
This is the new-style base class
This is the subclass of the NewStyle