What is the function of the self keyword in Python?

Discover Python self keywords: the key to object-oriented programming

In Python object-oriented programming, the self keyword is a special parameter in class methods, which often confuses beginners. This article will explain the meaning and importance of self in an easy-to-understand manner.

The following example shows two classes: MyClass and MyClass2 , both of which define myFunc method. MyClass ' myFunc method contains self parameter, while MyClass2 does not. After running the code, MyClass works normally, and MyClass2 throws TypeError exception, indicating that the number of parameters does not match. This is the key to self parameter.

self is not a Python syntax mandatory, but a programming convention. It represents the instance of the class itself. In an instance method, self is the first parameter, allowing the method to access and modify the instance properties. In MyClass , self.name = name assigns the value of the parameter name to name attribute of the instance myClass . Without self , the method cannot operate on instance properties.

The reason why myFunc method of MyClass2 is the lack of self parameter. The Python interpreter treats it as a static method, not an instance method, so there is no need to pass an instance object when invoking it. However, when trying to call this method through an instance object, an error of mismatch in the number of parameters. This highlights the role of self in distinguishing between instance methods and static methods.

In contrast to instance methods, static methods can be declared using the @staticmethod decorator. After adding @staticmethod in MyClass2 , the myFunc method becomes a static method, no longer requires self parameters, and can be called directly through the class name or instance object, indicating that the method has nothing to do with a specific instance.

To sum up, the self keyword is essentially a reference to the instance itself, allowing instance methods to access and modify instance properties, thereby realizing the core idea of ​​object-oriented programming - data encapsulation and method operations. The use of self is a convention of Python instance methods. The correct use of self is crucial to writing clear and maintainable code.

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