OOP principles overview in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Encapsulation in OOP?

Encapsulation means keeping data (attributes) and code (methods) together in one unit called a class. It hides the internal details and only exposes what is necessary.

beginner

Define Inheritance in simple terms.

Inheritance lets a new class use properties and methods from an existing class. It helps reuse code and create a hierarchy.

intermediate

What does Polymorphism mean in OOP?

Polymorphism means many forms. It allows different classes to use the same method name but behave differently depending on the class.

intermediate

Explain Abstraction with an example.

Abstraction hides complex details and shows only the important parts. For example, when you drive a car, you don’t need to know how the engine works, just how to use the steering and pedals.

beginner

Why are OOP principles useful in programming?

They help organize code better, make it reusable, easier to maintain, and model real-world things clearly.

Which OOP principle means hiding internal details and showing only necessary parts?

A Abstraction

B Inheritance

C Polymorphism

D Encapsulation

Abstraction hides complex details and shows only what is needed.

What does inheritance allow a class to do?

A Hide data from other classes

B Use methods and properties from another class

C Change method names dynamically

D Create many forms of the same method

Inheritance lets a class reuse code from a parent class.

Polymorphism allows methods to:

A Hide data inside a class

B Only show important details

C Create new classes from old ones

D Have the same name but behave differently

Polymorphism means many forms of the same method name.

Encapsulation is best described as:

A Using many classes

B Changing method behavior

C Keeping data and methods together inside a class

D Hiding complex details

Encapsulation bundles data and methods in one unit.

Which principle helps make code easier to maintain and reuse?

A All of the above

B Polymorphism

C Inheritance

D Abstraction

All OOP principles help improve code organization and reuse.

Describe the four main OOP principles and give a simple example for each.

Think about how a car works for abstraction.

Why is using OOP principles helpful when writing programs?

Imagine building with Lego blocks.

Practice

1. Which of the following is NOT one of the four main principles of Object-Oriented Programming (OOP)?

easy

A. Compilation

B. Inheritance

C. Polymorphism

D. Encapsulation

Solution

1. Step 1: Recall the four main OOP principles

   The four main principles are Encapsulation, Inheritance, Polymorphism, and Abstraction.

2. Step 2: Identify the option not in the list

   Compilation is a process related to converting code, not an OOP principle.

3. Final Answer:

   Compilation -> Option A

4. Quick Check:

   OOP principles exclude Compilation [OK]

Hint: Remember OOP principles: E, I, P, A [OK]

Common Mistakes:

• Confusing compilation with OOP concepts
• Mixing up abstraction with compilation
• Thinking all programming terms are OOP principles

2. Which Python keyword is used to create a new class?

easy

A. def

B. func

C. object

D. class

Solution

1. Step 1: Recall Python syntax for defining classes

   In Python, the keyword class is used to define a new class.

2. Step 2: Check other options

   def defines functions, object is a base class, and func is not a Python keyword.

3. Final Answer:

   class -> Option D

4. Quick Check:

   Use 'class' to define classes [OK]

Hint: Classes start with 'class' keyword in Python [OK]

Common Mistakes:

• Using def instead of class for classes
• Confusing object with class keyword
• Trying to use func which is invalid

3. What will be the output of this code?

class Animal:
    def speak(self):
        return "Sound"

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

pet = Dog()
print(pet.speak())

medium

A. Bark

B. Sound

C. None

D. Error

Solution

1. Step 1: Understand inheritance and method overriding

   Dog class inherits from Animal and overrides the speak method to return "Bark".

2. Step 2: Check which speak method is called

   pet is an instance of Dog, so pet.speak() calls Dog's speak method, returning "Bark".

3. Final Answer:

   Bark -> Option A

4. Quick Check:

   Overridden method returns 'Bark' [OK]

Hint: Child class method overrides parent method [OK]

Common Mistakes:

• Expecting parent class method output
• Confusing method overriding with overloading
• Thinking print outputs None

4. Find the error in this code snippet:

class Car:
    def __init__(self, model):
        self.model = model

    def display(self):
        print(Model)

medium

A. Constructor name is wrong

B. Missing self in display method

C. Model should be self.model in print

D. Class name should be lowercase

Solution

1. Step 1: Check the print statement inside display method

   The print statement uses Model which is undefined; it should use self.model to access the instance variable.

2. Step 2: Verify other parts

   The constructor name __init__ is correct, and method has self parameter. Class name capitalization is fine.

3. Final Answer:

   Model should be self.model in print -> Option C

4. Quick Check:

   Use self to access instance variables [OK]

Hint: Use self.variable to access instance data [OK]

Common Mistakes:

• Forgetting self in method parameters
• Using variable name without self prefix
• Thinking constructor name is incorrect

5. You want to create a class that hides its internal data and only allows access through methods. Which OOP principle does this demonstrate?

hard

A. Inheritance

B. Encapsulation

C. Polymorphism

D. Abstraction

Solution

1. Step 1: Understand the principle of hiding data

   Hiding internal data and controlling access through methods is called Encapsulation.

2. Step 2: Differentiate from other principles

   Inheritance is about reusing code, Polymorphism is about using methods in different ways, Abstraction is about hiding complexity but not necessarily data.

3. Final Answer:

   Encapsulation -> Option B

4. Quick Check:

   Data hiding = Encapsulation [OK]

Hint: Data hiding means Encapsulation [OK]

Common Mistakes:

• Confusing encapsulation with abstraction
• Mixing inheritance with data hiding
• Thinking polymorphism hides data