覆盖返回基类对象的方法 [英] overriding method that returns base class object

问题描述

我有一个来自第三方的A级，我无法更改

并且用C实现。我从A

派生我自己的B级并添加一对新方法并覆盖方法。

问题是A有一个方法（称之为A.f（）），它创建了

并返回一个新的A对象。我需要B.f（）来返回从A.f（）派生的B

对象。让

发生的最佳方法是什么？

I have a class A from a third party that I cannot change
and is implemented in C. I derive my own class B from A
and add a couple new methods and override a method. The
problem is that A has a method (call it A.f() ) that creates
and returns a new A object. I need B.f() to return a B
object derived from A.f(). What is the best way to make
that happen?

推荐答案

Stuart McGraw写道：

Stuart McGraw wrote:

我有来自第三方的A类，我无法改变
并在C中实现。我从A
派生了我自己的B类并添加了几个新方法并覆盖一个方法。问题是A有一个方法（称之为A.f（））创建
并返回一个新的A对象。我需要B.f（）来返回从A.f（）派生的B
对象。什么是使
发生的最佳方法？

I have a class A from a third party that I cannot change
and is implemented in C. I derive my own class B from A
and add a couple new methods and override a method. The
problem is that A has a method (call it A.f() ) that creates
and returns a new A object. I need B.f() to return a B
object derived from A.f(). What is the best way to make
that happen?

如果我理解正确，它与
$ b $无关事实上，父类是用C实现的，你只需要知道一些不常见的语法：


A类：

def f（个体经营）：

返回A（）


B级（A）：

def f（self ）：

obj = Af（自我）

＃做你想做的任何事情

返回obj


关键是你所说的来自Af（）的B对象。如果

派生你的意思与_inheritance_有关，那么

要么你不理解继承，要么你不清楚是什么

你想要的。


如果你只是想要B''sf（）做一些特别的事情

Af（）返回的对象，那么上面的代码应该让你

正确地做到这一点...


-Peter

If I understand this correctly, it has nothing to do with the
fact that the parent class is implemented in C and you just
need to know a little uncommon syntax:

class A:
def f(self):
return A()

class B(A):
def f(self):
obj = A.f(self)
# do whatever you want to obj here
return obj

The key is what you mean by "a B object derived from A.f()". If
by derived you mean something to do with _inheritance_, then
either you don''t understand inheritance or you weren''t clear what
you wanted.

If you just mean you want B''s f() to do something special to the
A object that A.f() returns, then the above code should let you
do that properly...

-Peter

对不起，你是对的，我不清楚。我的意思是B继承自

A.这是我想要做的......


A类有一个返回A的方法Aa（）我想要一个

相同的类但是有一个额外的属性.newprop

和方法.b（）我希望.a（）返回B，而不是A 。


B级（A）：

def __init __（自我，* args，** kwds）：

A. __init __（self，* args，** kwds）

self.newprop = 99

def a（self）：

x = Aa（self ）#x是A

x .__ class__ = B

返回x＃我希望x为B，即有b（）和.newprop。

def b（个体经营）：

......东西......


是的，我知道这是假的。但我不确定我应该做什么。并且为了纠正我最初发布的内容，A是在python中实现的（但我仍然不能因为管理原因而改变它的b $ b），但它的属性

声明为__ slots__ = [...]如果这产生了

的差异。这完全在Python 2.3.3中。

" Peter Hansen" < PE *** @ engcorp.com>在消息新闻中写道：40 *************** @ engcorp.com ...

Sorry, you are right, I wasn''t clear. I mean B inherits from
A. Here is what I am trying to do...

Class A has a method A.a() that returns an A. I want a
identical class but with an additional property .newprop
and method .b() And I want .a() to return a B, not an A.

class B (A):
def __init__(self, *args, **kwds):
A.__init__(self, *args, **kwds)
self.newprop = 99
def a(self):
x = A.a(self) # x is an A
x.__class__ = B
return x # I want x to be a B, i.e have b() and .newprop.
def b(self):
...something...

Yes, I know this is bogus. But I am not sure what
I should be doing. And to correct what I originally
posted, A is implented in python (but I still can''t
change it for administrative reasons), but it''s properties
are declared with "__slots__ = [...]" if that makes a
difference. This is all in Python 2.3.3.
"Peter Hansen" <pe***@engcorp.com> wrote in message news:40***************@engcorp.com...

Stuart McGraw写道：

Stuart McGraw wrote:

并在C中实现。我从A
派生我自己的B类并添加一些新方法并覆盖一个方法。问题是A有一个方法（称之为A.f（））创建
并返回一个新的A对象。我需要B.f（）来返回从A.f（）派生的B
对象。使
发生的最佳方法是什么？

I have a class A from a third party that I cannot change
and is implemented in C. I derive my own class B from A
and add a couple new methods and override a method. The
problem is that A has a method (call it A.f() ) that creates
and returns a new A object. I need B.f() to return a B
object derived from A.f(). What is the best way to make
that happen?

如果我理解正确的话，它与实现父类的事实无关在C和你只是需要知道一些不常见的语法：

def f（个体经营）：
返回A（）
se B级（A）：
def f（个体经营）：
obj = Af（个体经营）
＃做你想做的任何事情
返回obj

关键是你的意思是从Af（）得到的B对象。如果
派生你的意思与_inheritance_有关，那么
要么你不理解继承，要么你不清楚你想要什么。
如果你只是想要B''sf（）为Af（）返回的对象做一些特殊的事情，那么上面的代码应该让你这样做......

-Peter

If I understand this correctly, it has nothing to do with the
fact that the parent class is implemented in C and you just
need to know a little uncommon syntax:

class A:
def f(self):
return A()
se
class B(A):
def f(self):
obj = A.f(self)
# do whatever you want to obj here
return obj

The key is what you mean by "a B object derived from A.f()". If
by derived you mean something to do with _inheritance_, then
either you don''t understand inheritance or you weren''t clear what
you wanted.

If you just mean you want B''s f() to do something special to the
A object that A.f() returns, then the above code should let you
do that properly...

-Peter

文章< 40 ****************** ***@news.frii.net>，

Stuart McGraw< sm ****** @ frii.RemoveThisToReply.com>写道：

In article <40*********************@news.frii.net>,
Stuart McGraw <sm******@frii.RemoveThisToReply.com> wrote:

A类有一个返回A的方法Aa（）。我想要一个相同的类，但有一个额外的属性.newprop
和方法。 b（）我希望.a（）返回B，而不是A.

B类（A）：
def __init __（self，* args，** kwds）：
A .__ init __（self，* args，** kwds）
self.newprop = 99
def a（self）：
x = Aa（self）#x是一个A
x .__ class__ = B
返回x＃我希望x为B，即有b（）和.newprop。
def b（self）：
..某事......

是的，我知道这是假的。但是我不确定我应该做什么。
为了纠正我最初发布的内容，A在python中实现了
（但由于行政原因我仍然无法改变它），但它'声明的属性是用__ slots__ = [...]声明的。如果这会产生差异。这完全在Python 2.3.3中。

Class A has a method A.a() that returns an A. I want a
identical class but with an additional property .newprop
and method .b() And I want .a() to return a B, not an A.

class B (A):
def __init__(self, *args, **kwds):
A.__init__(self, *args, **kwds)
self.newprop = 99
def a(self):
x = A.a(self) # x is an A
x.__class__ = B
return x # I want x to be a B, i.e have b() and .newprop.
def b(self):
...something...

Yes, I know this is bogus. But I am not sure what I should be doing.
And to correct what I originally posted, A is implented in python
(but I still can''t change it for administrative reasons), but it''s
properties are declared with "__slots__ = [...]" if that makes a
difference. This is all in Python 2.3.3.

A类：

def a（个体经营）：

return self .__ class __（）

-

Aahz（aa**@pythoncraft.com）< *> http://www.pythoncraft.com/


争辩你的局限，果然他们是你的。 - 理查德巴赫

class A:
def a(self):
return self.__class__()
--
Aahz (aa**@pythoncraft.com) <*> http://www.pythoncraft.com/

"Argue for your limitations, and sure enough they''re yours." --Richard Bach

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