class Animal(object): def eat(self): print("动物吃东西") class Cat(Animal): def eat(self): print("猫吃鱼") # 格式一:父类名.方法名(对象) Animal.eat(self) # 格式二:super(本类名,对象).方法名() super(Cat, self).eat() # 格式三:super()方法名() super().eat() cat1 = Cat() cat1.eat() print(cat1)
#用元类实现单例模式 class SingletonType(type): instance = {} def __call__(cls, *args, **kwargs): if cls not in cls.instance: # 方式一: # cls.instance[cls] = type.__call__(cls, *args, **kwargs) # 方式二 # cls.instance[cls] = super(SingletonType, cls).__call__(*args, **kwargs) # 方式三 cls.instance[cls] = super().__call__(*args, **kwargs) return cls.instance[cls] class Singleton(metaclass=SingletonType): def __init__(self, name): self.name = name s1 = Singleton('1') s2 = Singleton('2') print(id(s1) == id(s2))
1. When a class has multiple inheritance, it inherits from multiple parents The classes have the same parent class A. When rewriting its parent class, you need to pay attention to
Method 1: Parent class name.Method name (object)
Parent class A Will be called multiple times (according to the number of inheritance)
Pass the required parameters as needed when overriding the parent class
Method 2 :super(class name, object).Method name()
The parent class A will only be called once
Rewrite the parent Class methods must pass all parameters
2. When a class has inheritance and the corresponding variables have been overridden in the subclass, changing the variables of the parent class will not affect the subclass.
class Parent(object): x = 1 class Child1(Parent): pass class Child2(Parent): pass print(Parent.x, Child1.x, Child2.x) Child1.x = 2 print(Parent.x, Child1.x, Child2.x) Parent.x = 3 print(Parent.x, Child1.x, Child2.x)
Output result
1 1 1
1 2 1
3 2 3
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