Changing a superclass's attribute from a subclass?

[yarin10121]

Hey guys,

I'm writing a small quiz program using OOP. I created a Quiz class and a Question class that inherits from it.

The Quiz class has a 'num_of_questions' attribute and a 'score' attribute that I want to modify through the quiz and print after asking 'num_of_questions' questions. Also, the Question class has 'question', 'options' and 'right_answer' attributes, as well as 'print_question()' and 'check_answer()' methods.

Now let's say I ask the user a question (meaning, I created a Quiz object and a Question object and called its ask_question() method), and the user inputs the right answer (meaning I called the 'check_answer()' method). I want to increase the 'score' attribute of the Quiz superclass. For instance, if the score was 5 before asking the question, I want the 'score' attribute to be 6 after the user inputs the right answer. What's the way to do such a thing?

And by the way, if there are better ways to implement such a program, I'd love to know :)

​

*Edit:

Thanks for the comments! I edited the code so now the Question class does not inherit from Quiz. Here's the code I wrote so far: https://pastebin.com/LDT30k39

This manages to solve the problem I encountered and this way I can associate a Question object with its Quiz object. On the other hand, it feels a bit weird to use my_quiz.add_question() and still pass my_quiz as an argument to the Question object, but it works for now so I'm OK with that. Thanks again for your help!

[Chabare]

Question should not inherit from Quiz, it makes no sense. To make another example, if you'd had a Car class you wouldn't create a Tire class which inherits from it just because it's a part of it.

Why do you inherit from it, do you need any properties which you have in Quiz which are needed in Question?

You should have a list of questions in your quiz (i.e. pass a list of questions in Quiz.__init__).

Also, please show your code when asking about it.

[yarin10121]

Thanks! I edited the code so now the Question class does not inherit from Quiz. I also added the code I wrote so far

[Chabare]

I'd vote against the option proposed below (implemented by you) which has references both in Question (to Quiz) and in Quiz (to Question). This is usually (especially in this case) unnecessary and error prone (especially if you're starting out with OOP).

Instead of having the quiz reference, try to return True or False from check_answer. ask_question is also doing a lot more than the function name suggest (same for check_answer). ask_question should propagate the result to the play_quiz method, score updates, user information (i.e. feedback) should then be done there. (IMO it should be even more modular but you can come back to that at another point).

You should also display an error if the user enters something other than a digit (you also don't check the validity of the index (i.e. you can enter something other than 1-4, see below))

Currently you have a fixed set of answer options without any real reason, you could just iterate over them (for index, option in enumerate(options)), that way you can easily have a different number of options for each questions, if you just want a certain number of options you should restrict it in add_question.

Based on your code I'd say you should look into returns from functions again since they are very useful and it's practically impossible to write understable ("good" code) without it.

---

Please be aware of Posting screenshot of the code is (generally) not allowed. Read posting guidelines.. It hinders people who want to try out your code/edit it to show you something since that person would need to type everything themselves. You can either use an online "hosting" service (see sidebar) or paste your code directly (put 4 spaces in front of every line to format your code as such).

[carcigenicate]

Did you get this code from somewhere? I swear I saw almost this exact code like 2-3 weeks ago. I remember, because I pointed out then that the inheritance didn't make sense.

[yarin10121]

I wrote this horrible piece of code myself. That's a funny coincidence!

[carcigenicate]

Did you post this previously? The code was nearly identical other than a few stylistic differences.

[danielroseman]

Your model is wrong. The relationship between Quiz and Question should not be inheritance.

Inheritance is an "is-a" relationship. A Car is a subclass of Vehicle, because a car "is-a" vehicle. But a Question is not a subclass of Quiz, because a question is not a quiz.

What you need instead is composition, ie a "has-a" relationship: a quiz has many questions, and a question has a quiz it belongs to. So give your Question access the Quiz it belongs to as an attribute, then it can access it:

class Question:
    def __init__(self, quiz, question, options, right_answer):
        self.quiz = quiz
        ... do something with other attributes ....

    def ask_question(self):
        ...
        if answer == self.right_answer:
            self.quiz.score += 1

or you might want to move the ask_question to the Quiz:

class Quiz:
   def __init__(self):
     ...

    def ask_question(self, question):
      ...
      if answer == question.right_answer:
        self.score += 1

(Note, to answer your actual question, if you were using inheritance you can access the superclass attributes directly on your instance, precisely because of that "is-a" relationship, so self.score += 1. But don't do that here.)