如何使用子类的默认值调用父类init？

Question

我试图给我的子类默认变量并在文件变胖时停止复制代码：

class Base(object):

    def __init__(self, username=None, password=None, start_url=None):
        self.username  = username
        self.password  = password
        self.start_url = start_url

class Subclass(Base):

    def __init__(self, username="hoss_it87", password="whatsgoodSO", start_url="www.boss-sauce.com"):
        super(Subclass, self).__init__()

Base当然有效，但我想Subclass以相同的方式初始化，只是None用真实的字符串覆盖（当然，所有登录样式都相似）。

In [12]: x = Base('myuser', 'mypassword', 'www.google.com')

In [13]: x.username
Out[13]: 'myuser'

In [14]: x.start_url
Out[14]: 'www.google.com'

In [15]: y = Subclass()

In [16]: y.username

In [17]: y.start_url

In [18]: y.password

In [19]: 

为什么我没有得到任何Subclass属性，我该如何解决？谢谢

请注意删除基类默认值会导致其他问题

class Base(object):

    def __init__(self, username, password, start_url):
        self.username  = username
        self.password  = password
        self.start_url = start_url

class Subclass(Base):

    def __init__(self, username="honeybooboosbiggestfan", password="toomuchburkerking", start_url="www.imjokingiprefericeroadtruckers.com"):
        super(Subclass, self).__init__()


In [24]: y = Subclass()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-24-55b9b4fdf93b> in <module>()
----> 1 y = Subclass()

<ipython-input-23-a9dc62450db7> in __init__(self, username, password, start_url)
      9 
     10     def __init__(self, username="honeybooboosbiggestfan", password="toomuchburkerking", start_url="www.imjokingiprefericeroadtruckers.com"):
---> 11         super(Subclass, self).__init__()

TypeError: __init__() takes exactly 4 arguments (1 given)

In [25]: 

解决了：

class Base(object):

    def __init__(self, username, password, start_url):
        self.username  = username
        self.password  = password
        self.start_url = start_url

class Subclass(Base):

    def __init__(self, username="honeybooboosbiggestfan", password="toomuchburkerking", start_url="www.imjokingiprefericeroadtruckers.com"):
        super(Subclass, self).__init__(username=username, password=password, start_url=start_url)

## -- End pasted text --

In [26]: y = Subclass()

In [27]: y.username
Out[27]: 'honeybooboosbiggestfan'

In [28]: 

Answer 1

您必须将参数从SubClassinit 传递到 init 块Base：

class Subclass(Base):

    def __init__(self, username="hoss_it87", password="whatsgoodSO", start_url="www.boss-sauce.com"):
        super(Subclass, self).__init__(username=username, password=password, start_url=start_url)

在您的代码中，Base调用 init 时不带参数，因此采用其默认参数，这些参数都是None.