了解继承

Question

我试图更好地理解继承。在下面的代码中，当我尝试打印friend.salary时，它会抛出一个AttributeError。 WorkingStudent是不是继承了Student类的所有方法？

class Student: 
    def __init__(self,name,school): 
     self.name = name 
     self.school = school 
     self.marks = [] 

    def average(self): 
     return sum(self.marks)/len(self.marks) 

    def friend(self,friend_name): 
     return Student(friend_name, self.school) 

anna = Student("Anna","MIT") 
friend = anna.friend("Motilal") 
#print (friend.name) 
#print (friend.school) 

class WorkingStudent(Student): 
    def __init__(self,name,school,salary): 
     super().__init__(self,name,school) 
     self.salary = salary 
     anna = WorkingStudent("Anna","SXS",25000) 
anna.friend("Greg") 
anna.marks.append(50) 
print friend.salary 

Answer 1

你应该修改源代码如下

class Student: 
    def __init__(self,name,school): 
     self.name = name 
     self.school = school 
     self.marks = [] 

    def average(self): 
     return sum(self.marks)/len(self.marks) 

    def friend(self,friend_name): 
     return Student(friend_name, self.school) 


anna = Student("Anna","MIT") 
friend = anna.friend("Motilal") 
#print (friend.name) 
#print (friend.school) 


class WorkingStudent(Student): 
    def __init__(self,name,school,salary): 
     super(WorkingStudent,self).__init__(name,school) 
     self.salary = salary 
     # anna = WorkingStudent("Anna","SXS",25000) 
    def friend(self,friend_name): 
     return WorkingStudent(friend_name, self.school, self.salary) 

# You should put your code here, because as your original code 
# anna is an instance of Student not WorkingStudent class 
# so it and its friend don't have "salary". 
anna = WorkingStudent("Anna","SXS",25000) # After this line, anna is a different variable to "anna" variable that was defined before (anna = Student("Anna","MIT")) 
friend = anna.friend("Greg") # friend now is an instance of WorkingStudent class, so it have salary 
anna.marks.append(50) 
print(friend.salary) 

Editted。所以代码现在可以工作