16.17. Group Work - Working with Multiple Classes

It is best to use a POGIL approach with the following. In POGIL students work in groups on activities and each member has an assigned role. For more information see https://cspogil.org/Home.

Note

If you work in a group, have only one member of the group fill in the answers on this page. You will be able to share your answers with the group at the bottom of the page.

Learning Objectives

Students will know and be able to do the following.

Content Objectives:

• Define a parent and child class.

• Predict the output from code with inheritance.

• Describe how a child can override an inherited method.

• Call the parent constructor

16.17.1. Inheritance

One class can inherit attributes and behavior from another class. The class that is inherited from is called the parent or base class. The one that is inheriting is called the child or derived class.

Run the following code

class Person: def __init__(self, first, last): self.first = first self.last = last def __str__(self): return("name: " + self.first + " " + self.last) def initials(self): return (self.first[0] + self.last[0]) class Employee(Person): def __init__(self, first, last, id): super().__init__(first, last) self.id = id def main(): p = Person("Barbara", "Ericson") print(p) print(p.initials()) p2 = Employee("Malik", "Abra", 7) print(p2) print(p2.initials()) main()

Look at the classes defined above. Then answer the following questions.

Q-6: Drag the code to the description of what it does Read the chapter on strings and try again
• super().__init__(first, last)
• Passes the first and last name to the parent class's __init__ method
• class Employee(Person):
• Defines a new class that inherits from the Person class
• def __init__(self, first, last):
• Defines an initializer (constructor) method
• def __str__(self):
• Defines a method that is called when you print an object of this class

Drag the blocks from the left and put them in the correct order on the right to define two classes: Car and SportsCar that inherits from Car. Add an __init__ method to the Car class that takes a make and sets the current object’s make. Add a __str__ method to the Car class and return a string with the make. Add an __init__ method to the SportsCar class that calls the parent class __init__ method.

        class Car:
---
    def __init__(self, make):
---
        self.make = make
---
    def __str__(self):
---
    def __str__(): #paired
---
        return "Car with make: " + self.make
---
class SportsCar(Car):
---
class SportsCar extends Car: #paired
---
    def __init__(self, make):
---
        super().__init__(make)
---
        super().__init__(self, make) #paired
        

Look at the code below and answer the following questions.

Run the following code

class Greeter: def __init__(self, message = "Good Morning"): self.message = message def greet(self): print(self.message) class Grump(Greeter): def __init__(self): super().__init__("Go Away") def main(): g1 = Greeter() g1.greet() print(g1) g2 = Grump() g2.greet() print(g2) main()

Q-11: What happens when a class doesn’t have a __str__ method and you print an object?

• You get an error
• It won't cause an error
• It prints None
• It doesn't print None
• It prints the type of the object (the class name)
• It prints the type of the object (the class name)
• It prints the variable name
• It does not print the variable name

Modify the code above to add a __str__ method to the Greeter class that returns the self.message and run the code again.

16.17.2. Overriding an Inherited Method

The child class can override an inherited method. This means it provides the same method name and parameter list as an inherited method.

Run the following code

class Student: def __init__(self, name): self.name = name def favorite_food(self): return "Pizza" class GradStudent(Student): def __init__(self, name): super().__init__(name) def favorite_food(self): return "Sushi" def main(): s1 = Student("Tiara") s2 = GradStudent("Carl") print(s1.favorite_food()) print(s2.favorite_food()) main()

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