Python：当需要参数[duplicate]时，使用super（）调用基类的__init __（）方法

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Python super() raises TypeError 4 answers

Python super()引发TypeError 4答案

I am trying to call the __init__() method in a superclass, where said method takes arguments, but it doesn't seem to be working. Please see the code below:

我试图在超类中调用__init __()方法,其中所述方法接受参数,但它似乎不起作用。请参阅以下代码:

>>> class A:
        def __init__(self, param1, param2):
            self._var1 = param1
            self._var2 = param2

>>> class B(A):
        def __init__(self, param1, param2, param3):
            super(B, self).__init__(param1, param2)
            self._var3 = param3


>>> a = A("Hi", "Bob")
>>> a._var1
'Hi'
>>> a._var2
'Bob'
>>> 
>>> b = B("Hello", "There", "Bob")

Traceback (most recent call last):
  File "<pyshell#74>", line 1, in <module>
    b = B("Hello", "There", "Bob")
  File "<pyshell#69>", line 3, in __init__
    super(B, self).__init__(param1, param2)
TypeError: must be type, not classobj
>>>

I have never been able to get this to work. What am I doing wrong? I would ideally like to use super() over A.__init__(self, <parameters>), if this is a possibility (which it must be).

我从来没有能够让这个工作。我究竟做错了什么?理想情况下,我喜欢使用super()而不是A .__ init __(self, ),如果这是可能的话(必须这样)。

3 个解决方案

#1

As a rule of thumb: in Python 2 your base class should always inherit from object, as otherwise you're using old style classes with surprising behaviors like the one you describe.

根据经验:在Python 2中,您的基类应始终从object继承,否则您将使用具有令人惊讶的行为的旧样式类,如您所描述的行为。

So try

class A(object):
    ...

like this:

In [1]: class A(object):
   ...:     def __init__(self, param1, param2):
   ...:         self._var1 = param1
   ...:         self._var2 = param2
   ...:

In [2]: class B(A):
   ...:     def __init__(self, param1, param2, param3):
   ...:         super(B, self).__init__(param1, param2)
   ...:         self._var3 = param3
   ...:

In [3]: a = A("Hi", "Bob")

In [4]: a._var1
Out[4]: 'Hi'

In [5]: a._var2
Out[5]: 'Bob'

In [6]: b = B("Hello", "There", "Bob")

In [7]: b._var3
Out[7]: 'Bob'

If you really know what you're doing (at least see the docs and this) and you want to use old-style classes you can't use super(), but instead need to manually call the super-class's __init__ from the sub class like this:

如果你真的知道你在做什么(至少看到文档和这个)并且你想使用旧式类你不能使用super(),而是需要从sub手动调用超类的__init__像这样的课:

class A:
    ...

class B(A):
    def __init__(self, p1, p2, p3):
        A.__init__(p1, p2)
        ...

#2

You can still use old style classes but in this case base class __init__ method should be called explicitly:

您仍然可以使用旧样式类,但在这种情况下,应该显式调用基类__init__方法:

class A:
    def __init__(self, param1, param2):
        self._var1 = param1
        self._var2 = param2

class B(A):
    def __init__(self, param1, param2, param3):
        A.__init__(self, param1, param2)
        self._var3 = param3

Test:

>>> b = B("Hello", "There", "Bob")
>>> b._var1
'Hello'
>>> b._var2
'There'
>>> b._var3
'Bob'
>>>

#3

The fix is to reference object class when declaring A

修复是在声明A时引用对象类

class A(object):
    def __init__(self, param1, param2):
        self._var1 = param1
        self._var2 = param2

This allows the script to execute successfully.

这允许脚本成功执行。

#1