{"id":2599,"date":"2021-10-21T01:24:24","date_gmt":"2021-10-21T01:24:24","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=2599"},"modified":"2025-03-31T09:03:46","modified_gmt":"2025-03-31T09:03:46","slug":"python-__del__","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-oop\/python-__del__\/","title":{"rendered":"Python __del__"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you will learn about the Python __del__<\/code> special method and understand how it works.<\/p>\n\n\n\n

Introduction to the Python __del__ method #<\/a><\/h2>\n\n\n\n

In Python, the garbage collector<\/a> manages memory automatically. The garbage collector will destroy the objects that are not referenced<\/a>.<\/p>\n\n\n\n

If an object implements the __del__<\/code> method, Python calls the __del__<\/code> method right before the garbage collector destroys the object.<\/p>\n\n\n\n

However, the garbage collector determines when to destroy the object. Therefore, it determines when the __del__<\/code> method will be called.<\/p>\n\n\n\n

The __del__<\/code> is sometimes referred to as a class finalizer. Note that __del__<\/code> is not the destructor because the garbage collector destroys the object, not the __del__<\/code> method.<\/p>\n\n\n\n

The Python __del__ pitfalls #<\/a><\/h2>\n\n\n\n

Python calls the __del__<\/code> method when all object references are gone. And you cannot control it in most cases.<\/p>\n\n\n\n

Therefore, you should not use the __del__<\/code> method to clean up the resources. It’s recommended to use the context manager.<\/p>\n\n\n\n

If the __del__<\/code> contains references to objects, the garbage collector will also destroy these objects when the __del__<\/code> is called.<\/p>\n\n\n\n

If the __del__<\/code> references the global objects, it may create unexpected behaviors.<\/p>\n\n\n\n

If an exception occurs inside the __del__<\/code> method, Python does not raise the exception but keeps it silent.<\/p>\n\n\n\n

Also, Python sends the exception message to the stderr. Therefore, the main program will be able to be aware of the exceptions during the finalization.<\/p>\n\n\n\n

In practice, you’ll rarely use the __del__<\/code> method.<\/p>\n\n\n\n

Python __del__ example #<\/a><\/h2>\n\n\n\n

The following defines a Person<\/code> class<\/a> with the special __del__<\/code> method, create a new instance of the Person<\/code>, and set it to None<\/a><\/code>:<\/p>\n\n\n

class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, age)<\/span>:<\/span>\n        self.name = name\n        self.age = age\n\n    def<\/span> __del__<\/span>(self)<\/span>:<\/span>\n        print('__del__ was called'<\/span>)\n\n\nperson = Person('John Doe'<\/span>, 23<\/span>)\nperson = None<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
__del__ was called<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
When we set the person<\/code> object to None<\/code>, the garbage collector destroys it because there is no reference. Therefore, the __del__<\/code> method was called.<\/p>\n\n\n\n
If you use the del<\/code> keyword to delete the person<\/code> object, the __del__<\/code> method is also called:<\/p>\n\n\n
person = Person('John Doe'<\/span>, 23<\/span>)\ndel<\/span> person<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
__del__ was called<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
However, the del<\/code> statement doesn’t cause a call to the __del__<\/code> method if the object has a reference.<\/p>\n\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n