I m trying to do a some activity on class obj destruction. How do I achive file open in _del__ function? (I m using 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")
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
Below code is work fine.
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")
In this case:
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")
When exit the __main__ function, before GC delete the "i" instance (execute i.__delete__) "open" function has remove from __builtins__.
As others have mentioned, don't use the ____del___ method to perform such cleanup. Instead, use either contextmanagers ( with -statement) or register atexit-handlers.
The problem is, as MuSheng tried to explain , that the __builtins__
are removed before your __del__
is called.
You can trigger the __del__
yourself by assigning None to the variable.
MuSheng's code could be this:
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")
MuSheng deserves some upvotes, IMO
Below is an alternate I used - Using atexit handlers:
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")
I m born
Script Ends. Now to GC clean memory
Done
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