__init__ raises an exception, then __del__ will still be called
issue 808164: socket.close() doesn't play well with __del__ - Python tracker https://bugs.python.org/issue808164
3. Data model — Python 3.8.3rc1 documentation https://docs.python.org/3/reference/datamodel.html#object.__del__
Re: __init__ and __del__
Guido.van.Rossum@cwi.nl
Tue, 18 May 1993 16:32:23 +0200
- Messages sorted by: [ date ][ thread ][ subject ][ author ]
- Next message: Guido.van.Rossum@cwi.nl: "Re: __init__ and __del__"
- Previous message: Chris Hoffmann: "__init__"
- In reply to: Chris Hoffmann: "__init__"
>From the responses so far I can conclude that having __init__
explicitly call the base class's __init__ is the best possible
solution, so let's move on to Chris' suggestion:
> By the way, will there be a __del__(self) method that is called at
> destruction time? My thought on this was that when python sees that an
> object should be garbage collected, it calls the object's __del__
> method (if any) before actually destroying it. Of course the
> interpreter would have to check the object's refcount after calling
> the function, as the method may have caused the object to be
> referenced by some other object.
The problem with this is, what to do if the __del__ call creates
another reference to the object? You can't delete it then since the
new reference would be dangling. But not deleting the object means
that the __del__ method may be called again later when the reference
count goes down to zero once again. Would this be a problem?
> I don't really have a good example of why you'd want this, other than
> for creating classes that keep track of how many instances of the
> class exist. Perhaps someone else can think of a good reason for
> having it. It just seems that if you have a function that is called at
> object creation that you should have one that is called at object
> destruction as well.
Actually, there are lots of situations where a class is used as a
wrapper around some "real-world" object (e.g. a window or a temporary
file or an audio device) that you would want to destroy (or restore to
a previous state) when the instance goes away. So yes, I think there
are many cases where this would be useful.
There's one problem with __del__, however: what if it raises an
exception? __del__ will be called implicitly from a DECREF(x)
statement in the C code, and I'm not going to add error checking to
all DECREF() statements. So these exceptions will have to be ignored.
In fact, there may already be an exception pending when DECREF() is
called, so it may have to save and restore the original exception.
Nasty!
One final thing to ponder: if we have a __del__ method, should the
interpreter guarantee that it is called when the program exits? (Like
C++, which guarantees that destructors of global variables are
called.) The only way to guarantee this is to go running around all
modules and delete all their variables. But this means that __del__
method cannot trust that any global variables it might want to use
still exist, since there is no way to know in what order variables are
to be deleted. Or is this not a useful feature?
--Guido van Rossum, CWI, Amsterdam <Guido.van.Rossum@cwi.nl>
- Next message: Guido.van.Rossum@cwi.nl: "Re: __init__ and __del__"
- Previous message: Chris Hoffmann: "__init__"
- In reply to: Chris Hoffmann: "__init__"
Python Gotchas 1: __del__ is not the opposite of __init__ | Algorithm.co.il http://www.algorithm.co.il/blogs/programming/python-gotchas-1-__del__-is-not-the-opposite-of-__init__/
class A:
def __init__(self, x):
if x == 0:
raise Exception()
self.x = x
def __del__(self):
print('__del__')
print(self.x)
A(1)
A(0)
Python Archives (1993): Re: __init__ and __del__ https://legacy.python.org/search/hypermail/python-1993/0109.html
class A:
def __init__(self, x):
if x == 0:
raise Exception()
self.x = x
def __del__(self):
print('__del__')
print(self.x)
A(1)
A(0)
__init__ raises an exception, then __del__ will still be called的更多相关文章
- python中__init__ ,__del__ &__new__
__new__ __new__方法是用来创建对象,__new__方法需要有一个返回值,这个返回值表示创建出来的对象的引用 __init__ __init__方法在类的一个对象被建立时 ,马上执行.__ ...
- Python构造器及析构器:__init__与__new__及__del__
__init__与__new__这两个魔法方法组成了Python类对象的构造器,在Python类实例化时,其实最先调用的不是__init__而是__new__.__new__是负责实例化对象的,而__ ...
- nested exception is java.lang.IllegalStateException: No persistence units parsed from {classpath*:META-INF/persistence.xml}
Deploying inside Eclipse v3.6 raises the exception. The WEB-INF/classes/ folder in the .war doesn't ...
- __del__()
__del__() 是类的内置函数,用于定义在脚本退出之前要执行的代码,因为有这个特性,通常被用来在脚本退出前关闭文件.关闭数据库连接.关闭网络连接等操作 [root@localhost ~]$ ca ...
- 描述符__get__,__set__,__delete__和析构方法__del__
描述符__get__,__set__,__delete__ 1.描述符是什么:描述符本质就是一个新式类,在这个新式类中,至少实现了__get__(),__set__(),__delete__()中的一 ...
- Python Exception处理
Python中的错误处理分为两类:语法错误和异常处理.语法错误一般是指由于python语句.表达式.函数等存在书写格式活语法规则上的错误抛出的异常,如python常见的缩进控制,若同层次的执行语句存在 ...
- C++ EH Exception(0xe06d7363)---捕获过程
书接上文<C++ EH Exception(0xe06d7363)----抛出过程>,下面我们讲下,VC++是如何catch到异常且处理的. 我们知道,在VC++里,C++异常实现的底层机 ...
- Python之路,Day8 - Python基础 面向对象高级进阶与socket基础
类的成员 类的成员可以分为三大类:字段.方法和属性 注:所有成员中,只有普通字段的内容保存对象中,即:根据此类创建了多少对象,在内存中就有多少个普通字段.而其他的成员,则都是保存在类中,即:无论对象的 ...
- 修改torndb库为依赖pymysql,使其适应python3,一个更简单的操作数据库的类。
1.python的MySQLdb和pymysql是两个基本数据库操作包,MySQLdb安装很麻烦,要有c++相关环境,python3也安装不了. python3一般安装pymysql,此包与MySQL ...
随机推荐
- SpringBoot进阶教程(六十八)Sentinel实现限流降级
前面两篇文章nginx限流配置和SpringBoot进阶教程(六十七)RateLimiter限流,我们介绍了如何使用nginx和RateLimiter限流,这篇文章介绍另外一种限流方式---Senti ...
- Semaphore信号量深度解析
1. 使用指南 package com.multthread; import java.util.concurrent.ExecutorService; import java.util.concur ...
- 读取 excel文件组装字典数据
package com.murong.ecp.app.mbu.action.bmbuurm8; import java.io.FileOutputStream;import java.io.Outpu ...
- CentOS安装TensorFlow
1.升级python 系统自带的python是2.6,不能用,升级到2.7,方法见:http://www.cnblogs.com/stAr-1/p/9055980.html 2.升级python带来的 ...
- [leetcode]380. Insert Delete GetRandom O(1)设计数据结构,实现存,删,随机取的时间复杂度为O(1)
题目: Design a data structure that supports all following operations in average O(1) time.1.insert(val ...
- mysql源码分析-启动过程
mysql源码分析-启动过程 概要 # sql/mysqld.cc, 不包含psi的初始化过程 mysqld_main: // 加载my.cnf和my.cnf.d,还有命令行参数 if (load_d ...
- spark:distinct算子实现原理
distinct的底层使用reducebykey巧妙实现去重逻辑 //使用reduceByKey或者groupbykey的shuffle去重思想rdd.map(key=>(key,null)). ...
- Mysql性能监控可视化
前言 操作系统以及Mysql数据库的实时性能状态数据尤为重要,特别是在有性能抖动的时候,这些实时的性能数据可以快速帮助你定位系统或Mysql数据库的性能瓶颈,镜像你在Linux系统上使用top.i ...
- vim_command
vi 打开vi空白面板 vi filename 以编辑模式打开文件.如果参数为已有文件,在vi中打开:如果参数为新文件名,在vi退出时提示用户保存编辑内容 vi -R filename 以只读模式打开 ...
- thinkphp3.2框架运行原理
thinkphp3.2是使用率非常普遍的国产php框架,以简单易于上手闻名,那么它框架结构是怎样的? tp3.2设计简单来说就是CBD,core(框架核心文件),bebavior(行为,tp3.2一大 ...