Python 在子类中调用父类方法详解（单继承、多层继承、多重继承）

 

by:授客 QQ：1033553122

 

测试环境：

win7 64位

Python版本：Python 3.3.5

代码实践：

1、在子类中通过“类名”调用父类的方法

class FatherA:

def __init__(self):

print('init action in father class A')

class SubClassB(FatherA):

def __init__(self):

print('init action in subclass B')

FatherA.__init__(self) # 在子类中调用父类的方法：父类名.方法名称(参数)

if __name__ == '__main__':

b = SubClassB()

运行结果：

>>> ================================ RESTART ================================

>>>

init action in subclass B

init action in father class A

缺点：当一个子类的父类发生变化时（如类SubClassB的父类由FatherA变为FatherD时），必须遍历整个类定义，把子类中所有的父类类名全部替换过来

2、在子类中通过“super”方法调用父类的方法

场景1、单层继承

class FatherA:

def __init__(self):

print('init action in father class A')

class SubClassB(FatherA):

def __init__(self):

print('init action in father class B')

super().__init__() # 在子类中调用父类的方法：super().方法名称(参数)

if __name__ == '__main__':

b = SubClassB()

class FatherA:

def __init__(self):

print('init action in father class A')

class SubClassB(FatherA):

def __init__(self):

print('init action in subclass B')

super(SubClassB, self).__init__()  # 在子类中调用父类的方法：super(type, obj).方法名称(参数)

if __name__ == '__main__':

b = SubClassB()

运行结果：

>>> ================================ RESTART ================================

>>>

init action in father class B

init action in father class A

说明：

1、super(type, obj)，其中obj必须是type类型、type子类类型的实例，否则会报错：

TypeError: super(type, obj): obj must be an instance or subtype of type

2、super().__init__()  效果等同 super(SubClassB, self). __init__()

场景2、多层继承

实验1：

class FatherA:

def __init__(self):

print('init action in father class A')

class SubClassB(FatherA):

def __init__(self):

print('init action in subclass B')

super().__init__()

class SubClassC(SubClassB):

def __init__(self):

print('init action in subclass C')

super().__init__()

if __name__ == '__main__':

b = SubClassC()

运行结果：

>>> ================================ RESTART ================================

>>>

init action in subclass C

init action in subclass B

init action in father class A

对比实验1-1：

class FatherA:

def __init__(self):

print('init action in father class A')

class SubClassB(FatherA):

def __init__(self):

print('init action in subclass B')

super().__init__()

class SubClassC(SubClassB):

def __init__(self):

print('init action in subclass C')

super(SubClassB, self).__init__()

if __name__ == '__main__':

b = SubClassC()

运行结果：

>>> ================================ RESTART ================================

>>>

init action in subclass C

init action in father class A

>>>

对比实验1-2：

class FatherA:

def __init__(self):

print('init action in father class A')

class SubClassB(FatherA):

def __init__(self):

print('init action in subclass B')

super().__init__()

class SubClassC(SubClassB):

def __init__(self):

print('init action in subclass C')

super(FatherA, FatherA).__init__(self) # 在子类中调用父类的方法：super(type, type).方法名称(参数)

if __name__ == '__main__':

b = SubClassC()

说明：可把 super(FatherA, FatherA).__init__(self) 换成：

super(FatherA, self).__init__()

或

super(FatherA, SubClassB).__init__(self)

或

super(FatherA, SubClassC).__init__(self)

注意：以上这种情况，必须给__init__传递参数self，否则会报错：

TypeError: __init__() missing 1 required positional argument: 'self'

运行结果：

>>> ================================ RESTART ================================

>>>

init action in subclass C

>>>

说明：super(type1, type2) ，type2必须和type1相同类型，或者其子类类型

实验2：

class FatherA:

def __init__(self):

print('init action in father class A')

class SubClassB(FatherA):

def __init__(self):

print('init action in subclass B')

super().__init__()

class SubClassC(SubClassB):

def __init__(self):

print('init action in subclass C')

super().__init__()

class SubClassD(SubClassC):

def __init__(self):

print('init action in subclass D')

super().__init__()

if __name__ == '__main__':

b = SubClassD()

运行结果：

>>> ================================ RESTART ================================

>>>

init action in subclass D

init action in subclass C

init action in subclass B

init action in father class A

对比实验2-1：

class FatherA:

def __init__(self):

print('init action in father class A')

class SubClassB(FatherA):

def __init__(self):

print('init action in subclass B')

super().__init__()

class SubClassC(SubClassB):

def __init__(self):

print('init action in subclass C')

super().__init__()

class SubClassD(SubClassC):

def __init__(self):

print('init action in subclass D')

super(SubClassB, self).__init__()

if __name__ == '__main__':

b = SubClassD()

运行结果：

>>> ================================ RESTART ================================

>>>

init action in subclass D

init action in father class A

>>>

对比实验2-2：

class FatherA:

def __init__(self):

print('init action in father class A')

class SubClassB(FatherA):

def __init__(self):

print('init action in subclass B')

super().__init__()

class SubClassC(SubClassB):

def __init__(self):

print('init action in subclass C')

super().__init__()

class SubClassD(SubClassC):

def __init__(self):

print('init action in subclass D')

super(SubClassC, self).__init__()

if __name__ == '__main__':

b = SubClassD()

运行结果：

>>> ================================ RESTART ================================

>>>

init action in subclass D

init action in subclass B

init action in father class A

通过对比实验2-1， 2-2，可看出super(type[,type2_or_obj]),type决定了super调用方法所在的父类--type的父类（如果有的话），即type决定了前往哪个父类调用指定的方法

场景3、多重继承

实验1：

class FatherA:

def __init__(self):

print('init action in father class A')

class FatherB:

def __init__(self):

print('init action in father class B')

class SubClassC(FatherA, FatherB):

def __init__(self):

print('init action in subclass C')

super(FatherB).__init__()

if __name__ == '__main__':

b = SubClassC()

运行结果：

>>> ================================ RESTART ================================

>>>

init action in subclass C

对比实验1-1：

class FatherA:

def __init__(self):

print('init action in father class A')

class FatherB:

def __init__(self):

print('init action in father class B')

class SubClassC(FatherB, FatherA):

def __init__(self):

print('init action in subclass C')

super().__init__()

if __name__ == '__main__':

b = SubClassC()

运行结果：

>>> ================================ RESTART
================================

>>>

init action in subclass C

init action in father class B

>>>

对比实验1-2：

class FatherA:

def __init__(self):

print('init action in father class A')

class FatherB:

def __init__(self):

print('init action in father class B')

class SubClassC(FatherA, FatherB):

def __init__(self):

print('init action in subclass C')

super().__init__()

if __name__ == '__main__':

b = SubClassC()

运行结果：

>>> ================================ RESTART
================================

>>>

init action in subclass C

init action in father class A

>>>

对比实验1-3：

class FatherA:

def __init__(self):

print('init action in father class A')

class FatherB:

def __init__(self):

print('init action in father class B')

class SubClassC(FatherA, FatherB):

def __init__(self):

print('init action in subclass C')

super(FatherB).__init__()

if __name__ == '__main__':

b = SubClassC()

>>> ================================ RESTART
================================

>>>

init action in subclass C

对比实验1-4：

class FatherA:

def __init__(self):

print('init action in father class A')

def testfn(self, arg):

print('testfn in father class A')

class FatherB:

def __init__(self):

print('init action in father class B')

def testfn(self):

print('testfn in father class B')

class SubClassC(FatherA, FatherB):

def __init__(self):

print('init action in subclass C')

super().testfn()

if __name__ == '__main__':

b = SubClassC()

运行结果：

>>> ================================ RESTART
================================

>>>

init action in subclass C

Traceback (most recent call last):

File
"C:/Users/Administrator/Desktop/1.py", line 21, in

b = SubClassC()

File
"C:/Users/Administrator/Desktop/1.py", line 18, in
__init__

super().testfn()

TypeError: testfn() missing 1 required positional
argument: 'arg'

>>>

对比实验1-5：

class FatherA:

def __init__(self):

print('init action in father class A')

def testfn(self):

print('testfn in father class A')

class FatherB:

def __init__(self):

print('init action in father class B')

def testfn(self, arg):

print('testfn in father class B')

class SubClassC(FatherA, FatherB):

def __init__(self):

print('init action in subclass C')

super().testfn()

if __name__ == '__main__':

b = SubClassC()

运行结果：

>>> ================================ RESTART
================================

>>>

init action in subclass C

testfn in father class A

说明：通过对比实验1-1，1-2，1-3，1-4，1-5可以看出，子类水平方向上，继承多个父类，以super().method(参数)方法调用父类的方法，如果不同父类中存在同名方法method(不管参数列表是否相同)，则按继承顺序，选择第一个父类中的方法。，如果想要调用多个方法咋办？如下，通过类名调用

class FatherA:

def __init__(self):

print('init action in father class A')

class FatherB:

def __init__(self):

print('init
action in father class B')

class SubClassC(FatherA, FatherB):

def __init__(self):

print('init action in subclass C')

FatherA.__init__(self)

FatherB.__init__(self)

if __name__ == '__main__':

b = SubClassC()

>>> ================================ RESTART
================================

>>>

init action in subclass C

init action in father class A

init action in father class B

>>>