Python上的类del [英] Python del on classes

问题描述

假设我们在python中有一个类：

  class A（object）：
 def __del __ ）：
 printDel！ 
  

__ del __ 任何 A 实例。

可以为类做同样的事吗？我想有一些方法调用时，类本身是垃圾收集，我假设是在脚本出口完成。

先感谢任何指针！

---

编辑：正如我的预期，每个人都试图驱使我远离使用这种技术（我可能会自己这样的评论:)），虽然问题仍然是：是可能吗？

我想要下面的内容：我有一个类需要清除静态成员。

  class A（object）：
 class Meta（type）：
 def __new __（mcs，name，bases，attrs）：
 attrs ['conn'] = sqlite3.connect（DB_FILE）
 return type .__ new __（mcs，name，bases，attrs）
 
 __metaclass__ = Meta 
  

我想要调用 A.conn.close（），但是在程序关闭之前 - 知道不会再创建 A 的实例。我知道我可以用 atexit 这样做，但这看起来很丑陋。

解决方案

问题是类包含循环引用回到自己 - 所以当它们被删除时，它们不容易收集 - 因此元类的 __ del __ 方法odf不被调用。

我可以使用Pypy的Python实现来触发它，但不使用cpython - 2.6或3.2。甚至触发，我不得不手动调用垃圾收集器 -
程序退出的Python环境已知是充满了不一致，并且 __ del __

这是我的Pypy会话，其中我触发了调用类 __ del __

 〜] $ pypy 
 Python 2.5.2（78826，2010年11月29日，00:18:05）
 [PyPy 1.4.0] on linux2 
输入help，copyright，credits了解更多信息。 
现在对于完全不同的东西：对不起，我会教仙人掌如何
后游
>>>> import gc 
>>>>> class Meta（type）：
 .... def __del __（cls）：
 .... print（Arghh !!）
 .... 
> >>>> class A（object）：
 .... __metaclass__ = Meta 
 .... 
>>>>> del A 
>>>>> gc.collect（）
 Arghh！ 
 0 
>>>>> 
  

Lets assume we have a class in python:

class A(object):
    def __del__(self):
        print "Del!"

__del__ is called upon deleting/garbage collection of any A instance.

Is is possible to do the same for a class? I would like to have some method called when the class itself is garbage collected, which I assume is being done at the script exit.

Thanks in advance for any pointers!

---

Edit: Just as I have expected, everyone is trying to drive me away from using this technique (I would probably make such a comment myself:)), though the question still stands: is it possible?

I want to the the following: I have a class with a static member that needs to be cleaned.

class A(object):
    class Meta(type):
        def __new__(mcs, name, bases, attrs):
            attrs['conn'] = sqlite3.connect( DB_FILE )
            return type.__new__(mcs, name, bases, attrs)

    __metaclass__ = Meta

I would like A.conn.close() to be called, but just before the program closes - i.e. when I know that no more instances of A will be ever created. I know I can do this with atexit, but this just seems very ugly.

解决方案

The problem is that classes contain circular references back to themselves - so when they are deleted they are not easily collected - thus the __del__ method odf the metaclass is not called.

I could trigger it being called using Pypy's Python implementation, but not using cpython - either 2.6 or 3.2. And even to trigger that, I had to manually invoke the garbage collector - The Python environment at program exit is known to be full of inconsitencies, and the chances of the __del__ method being called while enough internal information on the class would exist to allow a sae shut down would be very slim.

Here is my Pypy session where I did trigger the call to the class' __del__

 ~]$ pypy                                                                                       
Python 2.5.2 (78826, Nov 29 2010, 00:18:05)                                                                       
[PyPy 1.4.0] on linux2                                                                                            
Type "help", "copyright", "credits" or "license" for more information.                                            
And now for something completely different: ``sorry, I'll teach the cactus how                                    
to swim later''                                                                                                   
>>>> import gc
>>>> class Meta(type):         
....    def __del__(cls):                          
....       print ("Arghh!!")                                              
....                                                                      
>>>> class A(object):                                                                     
....   __metaclass__ = Meta                                                                                     
....                                                                                                                                                                                                                
>>>> del A                                                                                                        
>>>> gc.collect()                                                                                                 
Arghh!!                                                                                                           
0                                                                                                                 
>>>>

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