Class inheritance in python

Question

I am solving this problem :

Consider the following hierarchy of classes:

class Person(object): 
 def __init__(self, name): 
 self.name = name 
 def say(self, stuff): 
 return self.name + ' says: ' + stuff 
 def __str__(self): 
 return self.name 
class Lecturer(Person): 
 def lecture(self, stuff): 
 return 'I believe that ' + Person.say(self, stuff) 
class Professor(Lecturer): 
 def say(self, stuff): 
 return self.name + ' says: ' + self.lecture(stuff)
class ArrogantProfessor(Professor): 
 def say(self, stuff): 
 return 'It is obvious that ' + self.say(stuff)

As written, this code leads to an infinite loop when using the Arrogant Professor class.

Change the definition of ArrogantProfessor so that the following behavior is achieved:

e = Person('eric') 
le = Lecturer('eric') 
pe = Professor('eric') 
ae = ArrogantProfessor('eric')
e.say('the sky is blue') #returns eric says: the sky is blue
le.say('the sky is blue') #returns eric says: the sky is blue
le.lecture('the sky is blue') #returns believe that eric says: the sky is blue
pe.say('the sky is blue') #returns eric says: I believe that eric says: the sky is blue
pe.lecture('the sky is blue') #returns believe that eric says: the sky is blue
ae.say('the sky is blue') #returns eric says: It is obvious that eric says: the sky is blue
ae.lecture('the sky is blue') #returns It is obvious that eric says: the sky is blue

My solution to this is:

class ArrogantProfessor(Person):
 def say(self, stuff):
 return Person.say(self, ' It is obvious that ') + Person.say(self,stuff)
 def lecture(self, stuff):
 return 'It is obvious that ' + Person.say(self, stuff)

But the checker gives only half marks for this solution. What is the mistake that I am making and what are the test cases on which this code fails? (I am new to python and learned about classes some time ago.)

• L3viathan: Is that a typo in the solution for le.lecture(‘the sky is blue’), or is there really the pronoun "I" missing?
• sid597: @L3viathan that was a typo

Answer 1

You probably should use super() instead of hard-wiring the class Person:

class ArrogantProfessor(Person):
 def say(self, stuff):
 return super(ArrogantProfessor, self).say(self.lecture(stuff))
 def lecture(self, stuff):
 return 'It is obvious that ' + super(ArrogantProfessor, self).say(stuff)

Answer 2

It was given that:

class ArrogantProfessor(Professor): 

but you did this:

class ArrogantProfessor(Person): 

which resulted in the halved grade.

• sid597: Actually I first used Professor as the argument but that did not work so I changed that to Person
• gsamaras: That was the goal of the assigment @johnsmith! To make you think how to make it work with Professor. Good question btw, you got my upvote.

Answer 3

As a former grader of coding hw, I assume, you should have produced the desired output without making ArrogantProfessor a mere Person. After all, the class name indicates that it should still subclass Professor.

Answer 4

He probably wants you to actually get the parent class. The way to do this is simple.

Python2/3:

class ArrogantProfessor(Professor):
 def say(self, stuff):
 return 'It is obvious that ' + super(ArrogantProfessor, self).say(stuff)

Python 3 only:

class ArrogantProfessor(Professor):
 def say(self, stuff):
 return 'It is obvious that ' + super().say(stuff)

In either case, ae.say("something") should return:

"It is obvious that eric says: I believe that eric says: something"

This is because the parent class is Professor, not Person.

Similarly, in your lecture class, you should do:

def lecture(self, stuff):
 return 'I believe that ' + super(Lecturer, self).say(self, stuff) # or the Python3 version if you're using that

It's not really clear what it is that you want, though.

Answer 5

It's a bit hard to say without knowing what they're trying to teach you. A likely guess is that you're being taught inheritance, and if they've gone over super it's likely that they want you to utilize it to have the ArrogantProfessor's output look like:

eric says: It is obvious that STUFF

Where STUFF is the string you're passing in.

Answer 6

This should be:

class ArrogantProfessor( Professor ):
 def lecture(self, stuff):
 return 'It is obvious that ' + Person.say(self,stuff)

You don't have to define say() in ArrogantProfessor, because it is already defined in Professor, and it will use the lecture() method defined in the child class.

Answer 7

 class Professor(Lecturer): 
 def say(self, stuff): 
 return "Prof. " + self.name + ' says: ' + self.lecture(stuff)
 class ArrogantProfessor( Professor ):
 def lecture(self, stuff): 
 return 'It is obvious that I believe that ' + Person.say(self, stuff)

• Jeff: You should have context for your answer, not just code.

Answer 8

For the second part, the correct answer is:

class ArrogantProfessor(Professor):
 def lecture(self, stuff):
 return 'It is obvious that ' + Lecturer.lecture(self,stuff)

Answer 9

for part one the code is:

class ArrogantProfessor( Professor ):
def lecture(self, stuff):
 return 'It is obvious that ' + Person.say(self,stuff)

for part two the code is:

class ArrogantProfessor(Professor):
def lecture(self, stuff):
 return 'It is obvious that I believe that ' + Person.say(self,stuff)

for part three the code is:

class Professor(Lecturer):
 def say(self, stuff): 
 return 'Prof. ' + self.name + ' says: ' + self.lecture(stuff)

Hope it is usefull