如何存档 - 文件写在__del__上打开？

Question

我试图在类obj破坏上做一些活动。 如何在_del__函数中打开文件？ （我使用Python 3.4）

class iam(object):

    def __init__(self):
        print("I m born")

    def __del__(self):
        f = open("memory_report.txt", "w")
        f.write("He gone safe")
        f.close()

if __name__ == '__main__':
    i = iam()
    print("Script Ends. Now to GC clean memory")

输出：

I m born
Script Ends. Now to GC clean memory
Exception ignored in: <bound method iam.__del__ of <__main__.iam object at 0x00000000022F1A58>>
Traceback (most recent call last):
  File "F:\Kumaresan\Code\Python\CommonLib\src\kmxPyQt\devConsole3\tet.py", line 14, in __del__
NameError: name 'open' is not defined    

Answer 1

正如其他人所提到的，不使用____del___方法执行此类清理。相反，使用contextmanagers（ with -statement）或注册atexit-handlers。

Answer 2

下面的代码工作正常。

class iam(object):

def __init__(self):
    print("I m born")

def __del__(self):
    #"open" function still in __builtins__ 
    f = open("memory_report.txt", "w")
    f.write("He gone safe")
    f.close()

def write_iam():
        i=iam()

if __name__ == '__main__':
    write_iam()
    print("Script Ends. Now to GC clean memory")

在这种情况下：

class iam(object):

def __init__(self):
    print("I m born")

def __del__(self):
    #__builtins__.open  has remove 
    f = open("memory_report.txt", "w")
    f.write("He gone safe")
    f.close()

if __name__ == '__main__':
    i = iam()
    print("Script Ends. Now to GC clean memory")

退出__main__函数时，在GC删除＆＃34; i＆＃34;实例（执行i .__ delete__）＆＃34;打开＆＃34;函数已从__builtins __。

中删除

Answer 3

下面是我使用的替代方法 - 使用atexit处理程序：

import atexit


class iam(object):

    def __init__(self):
        print("I m born")
        atexit.register(self.cleanup)

    def cleanup(self):
        f = open("memory_report.txt", "w")
        f.write("He gone safe")
        f.close()
        print ("Done")


if __name__ == '__main__':
    i = iam()
    print("Script Ends. Now to GC clean memory")

输出：

I m born
Script Ends. Now to GC clean memory
Done

Answer 4

问题是，正如MuSheng尝试to explain，在调用 __builtins__之前删除了__del__。

您可以通过为变量指定“无”来自行触发__del__。

MuSheng的代码可能是这样的：

class iam():
    def __init__(self):
        print("I m born")

    def __del__(self):
        #"open" function still in __builtins__ 
        with open("memory_report.txt", "w") as f:
            f.write("He gone safe")

if __name__ == '__main__':
    i = iam()
    i = None # This triggers `__del__`
    print("Script Ends. Now to GC clean memory")

穆胜值得一些赞成，IMO