Define index assignment of objects using Python's __setitem__() function

Use Python's __setitem__() function to define the index assignment of objects

In Python, we can use __setitem__()Function to define the index assignment of the object. This function is a special method that is automatically called when assigning a value to an object. By overriding this method, we can customize the index assignment operation of the object.

The following is a simple example showing how to use the __setitem__() function to define the index assignment of an object:

class MyDict:
    def __init__(self):
        self.data = {}

    def __setitem__(self, key, value):
        self.data[key] = value
        print(f"设置 {key} 的值为 {value}")

    def __str__(self):
        return str(self.data)


my_dict = MyDict()
my_dict["foo"] = "bar"
my_dict["baz"] = 123

print(my_dict)

In the above code, we define a name is the class of MyDict. This class contains a dictionary attribute data as a container to store data.

We rewrite the __setitem__() function into a method, which has three parameters: self represents the object itself, key represents the setting The key, value represents the value to be set.

In the __setitem__() method, we store the key-value pair in the self.data dictionary and print a message to represent the setting operation of the key-value pair .

Next, we create an instance of the MyDict class my_dict. Then, we use dictionary-like syntax to perform index assignment on the my_dict object, such as my_dict["foo"] = "bar". Doing so will automatically call the __setitem__() method and perform the assignment operation we defined.

Finally, we print the contents of the my_dict object and observe the results.

Run the above code, the output will be:

设置 foo 的值为 bar
设置 baz 的值为 123
{'foo': 'bar', 'baz': 123}

As you can see, by customizing the __setitem__() function, we successfully defined the index assignment operation of the object , and provides customized control over the assignment process.

__setitem__()The application of the function is not limited to dictionaries. We can use it on other container type attributes in custom classes according to actual needs. This special method provides us with flexibility and extensibility, allowing us to define the index assignment behavior of objects according to our own design needs.

To summarize, use the __setitem__() function in Python to define the index assignment of an object. You can customize the assignment behavior of object attributes by overriding this special method. This allows us to more flexibly control the index assignment operation to meet our specific needs.

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