How to use the __new__() function to create an object instance in Python

How to use the __new__() function to create an object instance in Python

The __new__() function is a special method built into Python for creating object instances. Unlike the __init__() method, the __new__() method is called before the object is instantiated. It is responsible for creating the object and returning an instance of the object.

In Python, whenever an object instance is created, it is actually done by calling the __new__() method of the class. The __new__() method is responsible for creating an object instance, and in the process calls the __new__() method of its parent class, and finally returns a new object instance.

The following uses a code example to illustrate how to use the __new__() method to create an object instance.

class MyClass(object):
    def __new__(cls, *args, **kwargs):
        print("调用了__new__()方法")
        instance = super().__new__(cls)
        return instance
    
    def __init__(self, *args, **kwargs):
        print("调用了__init__()方法")
        # 对象初始化操作

# 创建对象实例
my_obj = MyClass()

In the above code, we define a class MyClass, which contains the __new__() and __init__() methods.

In the __new__() method, we first print a debugging information, and then create a new object instance by calling the super().__new__(cls) method, and This instance returns. Note that when calling super().__new__(cls), we passed cls as a parameter. This is because the __new__() method will receive a parameter cls, used to represent the current class.

Next, in the __init__() method, we also print a piece of debugging information, and then we can initialize the object as needed.

Finally, we call the constructor of MyClass to create the object instance my_obj.

When running the above code, we can see the following output:

调用了__new__()方法
调用了__init__()方法

As can be seen from the output, the __new__() method is called first, and then the __init__() method is called . This is because when creating an object instance, Python will first call the __new__() method to create the object, and then call the __init__() method to initialize the object.

It should be noted that the __new__() method is a class-level method, and the __init__() method is an object-level method. The __new__() method must return a new object instance, while the __init__() method does not need to return any value.

Therefore, by using the __new__() method, we can perform some special processing before the object is instantiated, such as controlling the creation process of the object, custom initializing the object, etc.

In summary, the __new__() method is a very powerful special method that can provide a more flexible way of creating objects in some cases. By mastering the use of the __new__() method, we can better understand Python's object-oriented programming and become more comfortable with the design and implementation of custom classes.

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