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This article mainly introduces "how to use the object destructor del in Python". In daily operation, I believe many people have doubts about how to use the object destructor del in Python. Xiaobian consulted all kinds of information and sorted out simple and easy operation methods. I hope to help you answer the doubts about "how to use the object destructor del in Python"! Next, please follow the small series to learn together!

Foreword:

The constructor__init__of classes in Python is called whenever an instance is generated.

Conversely, whenever an instance object needs to be reclaimed by garbage collection, the destructor__del__is used.

The__del__method is a special method of the class. The__del__method can be used to clean up resources, such as closing files.

Consider an example:

class Life: def __init__(self, name='None'): print('Hello,' + name) self.name = name def live(self): print(self.name) def __del__(self): print("Goodbye," + self.name)def main(): bob = Life('Bob') bob.live()if __name__ == '__main__': main()

Run this code and the output is:

Hello,Bob

Bob

Goodbye,Bob

We get the output above because the class Life is no longer needed when the code is near the end, so it is ready to be destroyed. The__del__method is automatically called before the class Life is destroyed.

You can also call the__del__method manually by calling del:

class Life: def __init__(self, name='None'): print('Hello,' + name) self.name = name def live(self): print(self.name) def __del__(self): print("Goodbye," + self.name)def main(): bob = Life('Bob') del bobif __name__ == '__main__': main()

Implementation results:

Hello,Bob

Goodbye,Bob

Note that del x does not directly call x.__ del__(), which decrements the reference count of x by one, while the latter is called only when its reference count reaches zero.

In Python, any unused object (such as an instance of a built-in type or class) is automatically deleted (removed) from memory when it is no longer in use. This process of freeing and reclaiming unused memory space is called garbage collection.

When is__del__used in Python?

It is important to note that when an object is in the process of destruction, the__del__method is called (uncorrupted), so properties can still be accessed in the__del__method.

Since__del__has access to the object's data members, you should ensure that the object's fill is deleted so that there is no memory leak.

class App: def __init__(self): print("Open App") def __del__(self): print("Closed App")class Phone: app = None def __init__(self): print("Switching on the Phone") self.__ class__.app = App() def __del__(self): del self.__ class__.app print("Switching off the Phone")phone = Phone()del phone

Implementation results:

Switching on the Phone

Open App

Closed App

Switching off the Phone

In this example, if we hadn't destroyed the phone's property app in the__del__method, it would have stayed in memory, causing a memory leak.

Destructor uses critical

Destructors in Python are not used as frequently as they are in C++ because of well-known warnings and a few little-known pitfalls.

Minimize the use of the__del__function:

First, because Python automatically reclaims all the memory space owned by an instance when it reclaims it, destructors don't need to consider space management. Therefore, the meaning of manually writing__del__is lost.

Second, it is impossible to predict when an instance will be recycled. Sometimes when you want to trigger a destructor, a reference to an object in the system table prevents the destructor from executing. Python also doesn't guarantee that an object that still exists will call its destructor when the interpreter exits.

Third, exceptions that__del__might throw print a warning message directly to sys.stderr (the standard error stream) rather than trigger an exception event. Because it runs through garbage collectors in unpredictable contexts.

Fourth, when we expect garbage collection, circular references between objects may prevent it from happening.

At this point, the study of "how to use the object destructor del in Python" is over, hoping to solve everyone's doubts. Theory and practice can better match to help everyone learn, go and try it! If you want to continue learning more relevant knowledge, please continue to pay attention to the website, Xiaobian will continue to strive to bring more practical articles for everyone!

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