python 当派生类找不到属性、方法时会怎么处理

python 当派生类找不到属性、方法时会怎么办

面试题之一。

class Parent(object):
    x = 1
    
class Child1(Parent):
    pass

class Child2(Parent):
    pass

print "Parent.x = ",Parent.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x

Child1.x = 2

print "Parent.x = ",Parent.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x

Parent.x = 3

print "Parent.x = ",Parent.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x

结果是：

Parent.x =  1 Child1.x =  1 Child2.x =  1
Parent.x =  1 Child1.x =  2 Child2.x =  1
Parent.x =  3 Child1.x =  2 Child2.x =  3

这道题终于做对了，因为记得，当派生类找不到对应的方法or属性时，会到基类那里去找。

而且是找最近的一个有这个属性的爸爸（爸爸去哪了）。

class GrandFather(object):
    x = 100
    y = 99


class Parent(GrandFather):
    x = 1
    
class Child1(Parent):
    pass


class Child2(Parent):
    pass


print "Parent.x = ",Parent.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x


Child1.x = 2


print "Parent.x = ",Parent.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x


Parent.x = 3


print "Parent.x = ",Parent.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x




print "Parent.y = ",Parent.y,"Child1.y = ",Child1.y,"Child2.y = ",Child2.y

结果先预测下，因为Parent已经有x了，所以Child1和Child2就找到Parent.x即可。

但是连Parent都没有y，所以Child1和Child2必须到GrandFather那里去才找到y属性。

结果：

Parent.x =  1 Child1.x =  1 Child2.x =  1
Parent.x =  1 Child1.x =  2 Child2.x =  1
Parent.x =  3 Child1.x =  2 Child2.x =  3
Parent.y =  99 Child1.y =  99 Child2.y =  99

咦，上面的是单继承，很简单的关系，万一是多继承呢，看看下面的孩子到底是随爸爸还是随妈妈？

class People(object):
    x = 100
    y = 99


class Father(People):
    x = 11


class Mother(People):
    x = 22




class Child1(Father,Mother):
    pass


class Child2(Father,Mother):
    pass


print "Father.x = ",Father.x,"Mother.x = ",Mother.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x


Child1.x = 2


print "Father.x = ",Father.x,"Mother.x = ",Mother.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x


Father.x = 33


print "Father.x = ",Father.x,"Mother.x = ",Mother.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x


Mother.x = 44


print "Father.x = ",Father.x,"Mother.x = ",Mother.x,"Child1.x = ",Child1.x,"Child2.x = ",Child2.x

结果：

Father.x =  11 Mother.x =  22 Child1.x =  11 Child2.x =  11
Father.x =  11 Mother.x =  22 Child1.x =  2 Child2.x =  11
Father.x =  33 Mother.x =  22 Child1.x =  2 Child2.x =  33
Father.x =  33 Mother.x =  44 Child1.x =  2 Child2.x =  33

啊，果然是随爸爸（作为一个大男人我感到很骄傲）。

总结：

1、派生类找不到属性or方法时，会向上寻找之，有该属性or方法的最近的那个。

2、多继承的继承顺序，感觉像是从左到右（好敷衍的总结呢）。