Polymorphism through inheritance in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is polymorphism in the context of inheritance?

Polymorphism means that a child class can use methods from its parent class but also change (override) them to behave differently. It allows one interface to be used for different underlying forms (data types).

beginner

How does method overriding demonstrate polymorphism?

Method overriding happens when a child class provides its own version of a method that already exists in the parent class. This lets the same method name do different things depending on the object calling it.

beginner

Consider this code snippet:<br><pre>class Animal:
    def sound(self):
        return "Some sound"

class Dog(Animal):
    def sound(self):
        return "Bark"

class Cat(Animal):
    def sound(self):
        return "Meow"</pre><br>What concept does this example show?

This example shows polymorphism through inheritance. The method sound is defined in the parent class Animal and overridden in child classes Dog and Cat to produce different sounds.

beginner

Why is polymorphism useful in programming?

Polymorphism lets us write flexible code that can work with different types of objects through a common interface. It helps reuse code and makes programs easier to extend and maintain.

beginner

What happens if a child class does not override a method from its parent?

If a child class does not override a method, it inherits the method from the parent class and uses it as is. This means the child class will behave like the parent for that method.

What does polymorphism allow in object-oriented programming?

A Using the same method name for different behaviors in child classes

B Creating multiple classes with the same name

C Preventing child classes from changing parent methods

D Writing code without any classes

Polymorphism allows methods with the same name to behave differently depending on the object calling them.

In Python, how do you override a method from a parent class?

A Use the 'override' keyword before the method

B Define a method with the same name in the child class

C Rename the method in the child class

D Call the parent method inside the child class

You override a method by defining a method with the same name in the child class.

If a child class does not override a parent method, what happens when the method is called on a child object?

A The parent class method is used

B An error occurs

C The method does nothing

D The child class automatically creates a new method

The child class inherits the parent method and uses it if it does not override it.

Which of these is an example of polymorphism through inheritance?

A Two classes have different method names

B A method is called without any class

C A class has only one method

D Different classes have a method with the same name but different code

Polymorphism means same method name, different behavior in different classes.

Why might a programmer use polymorphism?

A To avoid using classes

B To make code run faster

C To write code that works with many types of objects easily

D To prevent code reuse

Polymorphism helps write flexible code that can handle different object types through a common interface.

Explain polymorphism through inheritance in your own words and give a simple example.

Think about how child classes can change parent methods.

Describe why polymorphism is important for writing flexible and reusable code.

Consider how one method name can work differently for different objects.

Practice

1. What does polymorphism through inheritance allow in Python?

easy

A. One method name to have different behaviors in child classes

B. Multiple inheritance from unrelated classes

C. Using the same variable name in different functions

D. Creating objects without defining classes

Solution

1. Step 1: Understand polymorphism concept

   Polymorphism means one method name can behave differently depending on the class.

2. Step 2: Relate to inheritance

   Child classes override the method to provide their own behavior.

3. Final Answer:

   One method name to have different behaviors in child classes -> Option A

4. Quick Check:

   Polymorphism = One method, many behaviors [OK]

Hint: Polymorphism means same method, different actions [OK]

Common Mistakes:

• Confusing polymorphism with multiple inheritance
• Thinking polymorphism means same variable names
• Believing objects can exist without classes

2. Which of the following is the correct way to override a method in a child class?

easy

A. Call the parent method inside the child method without redefining

B. Use the keyword override before the method

C. Define a method with the same name in the child class

D. Rename the method in the child class

Solution

1. Step 1: Check method overriding syntax

   In Python, overriding means defining a method with the same name in the child class.

2. Step 2: Verify other options

   Python does not use override keyword; renaming is not overriding; calling parent method alone is not overriding.

3. Final Answer:

   Define a method with the same name in the child class -> Option C

4. Quick Check:

   Override = same method name in child [OK]

Hint: Override by redefining method name in child class [OK]

Common Mistakes:

• Using a non-existent override keyword
• Thinking calling parent method equals overriding
• Renaming method instead of overriding

3. What will be the output of this code?

class Animal:
    def sound(self):
        return "Some sound"

class Dog(Animal):
    def sound(self):
        return "Bark"

class Cat(Animal):
    def sound(self):
        return "Meow"

animals = [Dog(), Cat(), Animal()]
for a in animals:
    print(a.sound())

medium

A. Bark\nMeow\nSome sound

B. Some sound\nSome sound\nSome sound

C. Bark\nMeow\nError

D. Error\nError\nError

Solution

1. Step 1: Identify method overriding

   Dog and Cat classes override sound method to return "Bark" and "Meow" respectively.

2. Step 2: Trace the loop output

   Loop calls sound() on Dog(), Cat(), and Animal() objects, printing "Bark", "Meow", and "Some sound".

3. Final Answer:

   Bark Meow Some sound -> Option A

4. Quick Check:

   Overridden methods print their own sounds [OK]

Hint: Child method overrides parent, prints child's return [OK]

Common Mistakes:

• Assuming parent method always runs
• Expecting errors from calling base class method
• Mixing output order

4. Find the error in this code that tries to demonstrate polymorphism:

class Vehicle:
    def move(self):
        print("Moving")

class Car(Vehicle):
    def move(self):
        print("Driving")

class Bike(Vehicle):
    def move(self):
        print("Riding")

vehicles = [Car(), Bike()]
for v in vehicles:
    v.move

medium

A. List should include Vehicle() instance

B. Incorrect class inheritance syntax

C. Using print instead of return in methods

D. Missing parentheses when calling move method

Solution

1. Step 1: Check method calls in loop

   The code uses v.move without parentheses, so method is not called.

2. Step 2: Understand effect of missing parentheses

   Without parentheses, method object is referenced but not executed, so no output occurs.

3. Final Answer:

   Missing parentheses when calling move method -> Option D

4. Quick Check:

   Method call needs () to execute [OK]

Hint: Always add () to call methods [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Thinking print vs return causes error here
• Believing inheritance syntax is wrong

5. You want to add a new class Bird that also uses polymorphism with sound(). Which code correctly extends the existing classes and uses polymorphism?

hard

A. class Bird:
def sound(self):
return "Chirp"

animals.append(Bird())
for a in animals:
print(a.sound())

B. class Bird(Animal):
def sound(self):
return "Chirp"

animals.append(Bird())
for a in animals:
print(a.sound())

C. class Bird(Animal):
def noise(self):
return "Chirp"

animals.append(Bird())
for a in animals:
print(a.sound())

D. class Bird(Animal):
def sound(self):
print("Chirp")

animals.append(Bird())
for a in animals:
print(a.sound())

Solution

1. Step 1: Check inheritance and method name

   Bird must inherit from Animal and override sound() method to maintain polymorphism.

2. Step 2: Verify method behavior and usage

   Method returns string "Chirp" like others; appending Bird() to animals list and calling sound() works correctly.

3. Final Answer:

   Correctly inherits Animal and overrides sound() returning "Chirp" -> Option B

4. Quick Check:

   Polymorphism needs same method name and inheritance [OK]

Hint: Inherit and override same method name with matching signature [OK]

Common Mistakes:

• Not inheriting from Animal class
• Using different method name like noise()
• Printing inside method instead of returning