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Python oop - class 2 (inheritance)
This document discusses object-oriented programming concepts in Python, including inheritance and method overriding. It provides examples of using inheritance to create child classes like Taxi and Bus that inherit attributes and methods from a parent Vehicle class. It also demonstrates overriding the __init__ and __str__ methods in child classes to customize initialization and string representation while still calling the parent methods. The document includes exercises for readers to practice modeling inheritance relationships and method overriding.
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Python oop - class 2 (inheritance)
- 1. Object Oriented Programmingin Python: Inheritance principles Aleksander Fabijan September 2018
- 2. Today’s Goals 1. Providean introduction to inheritance in OOP. • Why and when should we inherit from other objects? • How do we inherit from objects in Python? 2. Provide an introduction to method overriding.
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- 5. Comparing Bus &Taxi
- 6. Comparing Bus &Taxi Classes share similar variables
- 7. Inheritance • Inheritance simplifiesour code through reuse of the code that has been already written. • Think about the Taxi and Bus, and what they have in common. • Inheritance is a relation between a parent class (e.g. Vehicle) and children classes (e.g. Taxi, Bus, Truck, etc.) • A class inherits attributes and behavior methods from its parent classes.
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- 9. Taxi DriverName NumberOfWheels NumberOfSeats OnDuty Bus DriverName NumberOfWheels NumberOfSeats Color Wait, we wrotethe same three lines of code in both classes? There must be a better way!!!
- 10. Vehicle DriverName NumberOfWheels NumberOfSeats Taxi OnDuty Bus Color We moved thecommons in a parent class The child classes only keep the attributes and methods relevant to them
- 11. OOP Inheritance inPython 1. Create a parent class (e.g. Vehicle) with the common attributes and common methods. 2. Create child classes (e.g. Bus and Taxi) with the extended attributes and extended methods. • Pass the class definition to the child (e.g. Class Bus(Vehicle): …) • Use the parent attributes and methods through super().
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- 17. Exercise time! Model thefollowing problem in Python code: • Frida Jacobsson is a student at MAH. Her Skype nickname is frida96. • Aleksander Fabijan is a researcher at MAH. He teaches DA712 and DA374. • They are both Humans.
- 18. Exercise time! Model thefollowing problem in Python code: • Frida Jacobsson is a Student at MAH. Her Skype nickname is frida96. • Aleksander is a Researcher at MAH. He teaches DA712 and DA374. • They are both Humans. Suggestion: 1) Create a class Human that initiates a new human with a name. 2) Next, create two classes (e.g. Student and Researcher) that inherit from human, 3) Finally, add the skype nickname and the list of courses to the new classes. Code snippets for help: • class Taxi(Vehicle): #creates a child class from Human • super().__init__(name, lastname) #calls the parent’s __init__method
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- 20. Method Overriding • Methodoverriding is an object-oriented programming feature that allows a subclass to provide a different implementation of a method that is already defined by its superclass or by one of its superclasses. • __init__ in the child class (e.g. Taxi) overrides the __init__ method from the parent class.
- 21. Example of overriding__str__ Let’s add a __str__ method that nicely prints our Vehicle details on the screen. Output:
- 22. Example of overriding__str__
- 23. Example of overriding__str__
- 24. Exercise Time Part1: Updateyour class Human with a __str__ method that can be used on print. It should return the name and lastname of the human. Try it out by creating one human in code. Part2: Update your class student and class researcher by overriding the __str__ method. • __str__ in the child classes should use super().__str__(args) to call its parent method to print out the name and lastname. Part3: For student, override the __str__(args) method so it returns in addition to the name and lastname, also the skype nickname. Do the same for the researcher with his phone extension.
- 25. Takeaways Today, we learnedhow and when to use inheritance in python OOP. • Whenever our classes can reuse the attributes and methods from parent classes. • We inherit from parent classes by passing their name as a parameter to our child class. • We reuse the methods and attributes from parent classes by using super(). We also learned how to override methods in python.