如何使用子类中的默认值调用父类 init

Question

我正在尝试为我的子类提供默认变量并停止复制代码，因为文件越来越胖：

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，但我希望Subclass以相同的方式初始化，只是用真正的字符串覆盖None(当然，所有登录样式都是相似的(。

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Subclass属性，我该如何解决它？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：

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

你必须将参数从 SubClass init 传递给 Base 的 init 块：

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，调用 init Base时不带参数，因此采用其默认参数，这些参数都是None的。