python中__init__方法是做什么的_Python类中__init__构造方法详解

class age-default'>age-default'>Person:     def age-default'>age-default'>age-default'>age-default'>age-default'>age-default'>__init__(self, age-default'>name, age):         self.age-default'>name = age-default'>name         self.age = age      def greet(self):         return f"Hello, my age-default'>name is {self.age-default'>name} and I am {self.age} years old."  person1 = age-default'>age-default'>Person("Alice", 30) person2 = age-default'>age-default'>Person("Bob", 25)  print(person1.greet())  # 输出: Hello, my age-default'>name is Alice and I am 30 years old. print(person2.greet())  # 输出: Hello, my age-default'>name is Bob and I am 25 years old. 

age-default'>name

age

self.age-default'>name

self.age

class Rectangle:     def age-default'>age-default'>age-default'>age-default'>age-default'>age-default'>__init__(self, width, height=10):         self.width = width         self.height = height      def area(self):         return self.width * self.height  rect1 = Rectangle(5)  # height 使用默认值 10 rect2 = Rectangle(5, 20) # height 显式设置为 20  print(rect1.area())  # 输出: 50 print(rect2.area())  # 输出: 100

Rectangle

class Circle:     def age-default'>age-default'>age-default'>age-default'>age-default'>age-default'>__init__(self, radius):         if radius <= 0:             raise ValueError("Radius must be positive")         self.radius = radius         self.area = 3.14159 * radius * radius      def describe(self):         return f"Circle with radius {self.radius} and area {self.area}"  try:     circle1 = Circle(-5) # 抛出 ValueError except ValueError as e:     print(e) # 输出: Radius must be positive  circle2 = Circle(3) print(circle2.describe()) # 输出: Circle with radius 3 and area 28.27431

radius

ValueError

self.area

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class Singleton:     _instance = None      def __new__(cls, *args, **kwargs):         if not cls._instance:             cls._instance = super().__new__(cls, *args, **kwargs)         return cls._instance      def age-default'>age-default'>age-default'>age-default'>age-default'>age-default'>__init__(self, age-default'>name):         self.age-default'>name = age-default'>name  s1 = Singleton("First") s2 = Singleton("Second")  print(s1.age-default'>name)  # 输出: First print(s2.age-default'>name)  # 输出: First  (因为 s1 和 s2 是同一个实例) print(s1 is s2) # 输出: True

Singleton

Singleton()

class Animal:     def speak(self):         print("Generic animal sound")  class Dog(Animal):     def speak(self):         print("Woof!")  dog = Dog() dog.speak() # 输出: Woof!

Animal

super()

class Vehicle:     def age-default'>age-default'>age-default'>age-default'>age-default'>age-default'>__init__(self, make, model):         self.make = make         self.model = model      def describe(self):         return f"Vehicle: {self.make} {self.model}"  class Car(Vehicle):     def age-default'>age-default'>age-default'>age-default'>age-default'>age-default'>__init__(self, make, model, num_doors):         super().age-default'>age-default'>age-default'>age-default'>age-default'>age-default'>__init__(make, model)         self.num_doors = num_doors      def describe(self):         return f"{super().describe()}, {self.num_doors} doors"  car = Car("Toyota", "Camry", 4) print(car.describe()) # 输出: Vehicle: Toyota Camry, 4 doors

Car

super().age-default'>age-default'>age-default'>age-default'>age-default'>age-default'>__init__(make, model)

Vehicle

make

model

num_doors

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