如何在子类中重写父类的类变量？

在子类中重写父类的类变量，核心是给子类定义同名的类变量（或通过子类名动态赋值），让子类拥有独立的类变量，不再共享父类的同名变量。下面分「静态重写」「动态重写」两种场景，结合示例讲透具体操作、效果和避坑点。

一、核心原理

父类的类变量会被子类继承，若子类未定义同名变量，访问子类 / 子类实例的该变量时，会读取父类的；若子类定义了同名类变量（重写），子类会在自己的命名空间中创建独立变量，与父类解耦，后续修改子类的该变量不会影响父类。

二、场景 1：静态重写（定义子类时直接声明）

这是最常用的方式 —— 在子类定义时，直接声明与父类同名的类变量，完成重写。

示例：基础静态重写

python

运行

class Parent: # 父类类变量 brand = "父类默认品牌" max_count = 10 class Child(Parent): # 重写：子类声明同名类变量，覆盖父类的 brand = "子类定制品牌" # 可只重写部分变量（如只重写brand，保留max_count） # 验证重写效果 print(Parent.brand) # 输出：父类默认品牌（父类不变） print(Child.brand) # 输出：子类定制品牌（子类用自己的） print(Child.max_count) # 输出：10（未重写，仍继承父类） # 修改子类重写后的变量，不影响父类 Child.brand = "子类修改后的品牌" print(Child.brand) # 输出：子类修改后的品牌 print(Parent.brand) # 输出：父类默认品牌（不受影响）

示例：重写可变类型类变量

若父类类变量是列表、字典等可变类型，子类重写时需赋值新的可变对象，而非修改父类对象的内部元素：

python

运行

class Parent: # 父类可变类变量 items = [1, 2, 3] class Child(Parent): # 重写：赋值新的列表（子类独立变量） items = [10, 20, 30] # 验证 print(Parent.items) # 输出：[1,2,3]（父类不变） print(Child.items) # 输出：[10,20,30]（子类自己的） # 修改子类变量的内部元素，仅影响子类 Child.items.append(40) print(Child.items) # 输出：[10,20,30,40] print(Parent.items) # 输出：[1,2,3]（父类不受影响）

三、场景 2：动态重写（运行时赋值）

若需要在程序运行时（而非定义子类时）重写父类类变量，可通过「子类名。变量名 = 新值」动态赋值，效果与静态重写一致。

示例：动态重写类变量

python

运行

class Parent: version = "1.0" config = {"mode": "normal"} class Child(Parent): # 初始未重写，继承父类的version和config pass # 运行时动态重写单个变量 Child.version = "2.0" print(Child.version) # 输出：2.0（子类独立变量） print(Parent.version) # 输出：1.0（父类不变） # 动态重写可变类型变量（赋值新对象） Child.config = {"mode": "debug", "timeout": 10} print(Child.config) # 输出：{'mode': 'debug', 'timeout': 10} print(Parent.config) # 输出：{'mode': 'normal'}（父类不变）

四、场景 3：在子类方法中重写 / 修改重写后的类变量

子类重写类变量后，在子类的实例方法 / 类方法中修改时，需用「子类名。变量名」，而非self（self赋值会创建实例变量）。

示例：子类方法中操作重写后的类变量

python

运行

class Parent: count = 0 class Child(Parent): # 静态重写类变量 count = 100 def add_count(self): # 正确：修改子类自己的类变量 Child.count += 1 def wrong_add(self): # 错误：self.count +=1 → 给实例新增count变量，而非修改类变量 self.count += 1 # 验证正确操作 c = Child() c.add_count() print(Child.count) # 输出：101（子类类变量已改） print(c.count) # 输出：101（读子类类变量） # 验证错误操作 c.wrong_add() print(c.count) # 输出：102（实例变量） print(Child.count) # 输出：101（子类类变量未变）

五、重写的避坑点

1. 不要通过实例重写类变量：子类实例.变量名 = 新值只会给实例新增同名实例变量，不会重写子类的类变量；

   python

   运行

   c = Child() c.brand = "实例临时值" print(c.brand) # 输出：实例临时值（实例变量） print(Child.brand) # 输出：子类定制品牌（子类类变量未变）

2. 可变类型变量避免 “修改父类元素”：若子类未重写，直接修改父类可变变量的内部元素（如Child.items.append(4)），会影响父类和所有未重写的子类，这不是 “重写”，而是 “修改父类变量”；
3. 不要滥用双下划线命名：父类类变量若用双下划线开头（如__var），会触发名称改写（变成_Parent__var），子类需用_Parent__var才能访问，重写时易出错，非必要不要用。

六、重写 vs 继承：核心对比

总结：子类重写父类类变量的 3 条核心规则

1. 静态重写：定义子类时直接声明同名类变量；
2. 动态重写：运行时通过子类名.变量名 = 新值赋值；
3. 可变类型：重写时必须赋值新的可变对象（如[]/{}），而非修改父类对象的内部元素。

只要遵循「子类名绑定新值」的原则，就能实现类变量的重写，让子类拥有独立的类级属性。

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