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.)

Is that a typo in the solution for le.lecture(‘the sky is blue’), or is there really the pronoun "I" missing? — L3viathan
– L3viathan, Commented Mar 12, 2016 at 22:31

Mike Müller · Accepted Answer · 2016-03-12 23:28:21Z

7

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)

edited Mar 12, 2016 at 23:28

answered Mar 12, 2016 at 22:51

Mike Müller

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Comments

gsamaras · Accepted Answer · 2016-03-12 22:52:58Z

4

It was given that:

class ArrogantProfessor(Professor):

but you did this:

class ArrogantProfessor(Person):

which resulted in the halved grade.

answered Mar 12, 2016 at 22:52

gsamaras

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2 Comments

sid597 Over a year ago

Actually I first used Professor as the argument but that did not work so I changed that to Person

gsamaras Over a year ago

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.

user2390182 · Accepted Answer · 2016-03-12 22:52:00Z

2

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.

answered Mar 12, 2016 at 22:52

user2390182

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Comments

Goodies · Accepted Answer · 2016-03-12 22:52:16Z

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.

willnx · Accepted Answer · 2016-03-12 22:54:05Z

2

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.

answered Mar 12, 2016 at 22:54

willnx

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Comments

Vasili Korol · Accepted Answer · 2016-03-12 23:07:54Z

2

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.

edited Mar 12, 2016 at 23:07

answered Mar 12, 2016 at 22:53

Vasili Korol

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Comments

Laurent Rouchairoles · Accepted Answer · 2016-03-14 13:28:26Z

0

     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)

answered Mar 14, 2016 at 13:28

Laurent Rouchairoles

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1 Comment

Jeff Over a year ago

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

IgorMatkovic · Accepted Answer · 2016-03-15 10:50:25Z

0

For the second part, the correct answer is:

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

answered Mar 15, 2016 at 10:50

IgorMatkovic

11 silver badge

Comments

Jean · Accepted Answer · 2016-03-15 14:03:49Z

0

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

answered Mar 15, 2016 at 14:03

Jean

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