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
>>>