1. Constructor

1. Member variable assignment problem

In the previous blog, the defined Python class Student:

class Student:
    name = None  # 姓名
    age = None  # 年龄

    def info(self):
        print(f"姓名 : {
      
      self.name} , 年龄 : {
      
      self.age}")

If you want to assign values to its member variables, you need to assign values to the two member variables name and age respectively,

s = Student()
s.name = "Tom"
s.age = 18

For the above 2 variables, 2 lines of code are written. If there are more than a dozen variables, then more than a dozen lines of code are needed to complete the operation of member variable assignment;

2. Introduction of construction method

Using the construction method, you can assign values to multiple variables at the same time in one line of code , which can reduce the amount of code;

Introduction to the construction method:

Constructor function name: The constructor of the Python class is __init__()the method, and the name of the method inithas two underscores before and after the word _;
Construction method call timing: when creating an instance object of a class, the construction method of the Python class will be automatically executed __init__();
Construction method parameters: When creating an object, if parameters are passed in, the parameters will be automatically passed to __init__()the construction method for use;

3. Code example - construction method

In the code below, the Student class contains __init__constructors, and infomember methods;

__init__()In the construction method, two parameters name and age are received and assigned to name and age member variables respectively;

In info() the method, print the student's name and age members to the console;

Code example:

"""
面向对象 代码示例
"""


class Student:
    name = None  # 姓名
    age = None  # 年龄

    def __init__(self, name, age):
        self.name = name
        self.age = age

    def info(self):
        print(f"姓名 : {
      
      self.name} , 年龄 : {
      
      self.age}")


s = Student("Tom", 18)
s.info()

Results of the :

D:\001_Develop\022_Python\Python39\python.exe D:/002_Project/011_Python/HelloPython/Hello.py
姓名 : Tom , 年龄 : 18

Process finished with exit code 0

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3. The constructor can define member variables at the same time

In the above code example, the name and age member variables are defined,

class Student:
    name = None  # 姓名
    age = None  # 年龄

These two member variables can be omitted;

The constructor also has another function, which is to define member variables and assign values to them;

    def __init__(self, name, age):
        self.name = name
        self.age = age

In the following code, no member variable is defined, and __init__()the value is assigned directly in the construction method;