Software engineering principles - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the principle of Modularity in software engineering?

Modularity means breaking a software system into smaller, independent parts called modules. Each module handles a specific task, making the system easier to understand, develop, and maintain.

beginner

Explain the DRY (Don't Repeat Yourself) principle.

DRY means avoiding duplication of code or logic. Instead of repeating the same code, you write it once and reuse it. This reduces errors and makes maintenance easier.

intermediate

What does the Single Responsibility Principle (SRP) state?

SRP says that each part of a program should have only one reason to change. In other words, a module or class should focus on a single task or responsibility.

beginner

Why is Testing important in software engineering?

Testing helps find and fix errors early. It ensures the software works as expected and improves quality and reliability before users see it.

intermediate

Describe the Open/Closed Principle.

This principle means software entities like classes should be open for extension but closed for modification. You can add new features without changing existing code, reducing bugs.

Which principle encourages breaking software into smaller parts?

A Testing

B DRY

C Open/Closed Principle

D Modularity

Modularity is about dividing software into smaller, manageable modules.

What does DRY stand for?

A Don't Repeat Yourself

B Do Repeat Yourself

C Debug Regularly Yourself

D Design Right Yourself

DRY means 'Don't Repeat Yourself' to avoid code duplication.

The Single Responsibility Principle means:

A A module should have many responsibilities

B Modules should be open for modification

C A module should have only one reason to change

D Modules should be tested once

SRP states each module should focus on a single responsibility.

Why is testing done in software engineering?

A To add new features

B To find and fix errors early

C To write more code

D To increase software size

Testing helps find and fix errors before software release.

The Open/Closed Principle means software should be:

A Open for extension, closed for modification

B Open for modification, closed for extension

C Closed for both extension and modification

D Closed for extension, open for modification

It means software can be extended without changing existing code.

Explain the importance of modularity and how it helps in software development.

Think about how dividing a big task into smaller tasks helps.

Describe the DRY principle and why avoiding code duplication is beneficial.

Imagine fixing a bug in one place instead of many.

Practice

1. Which software engineering principle encourages writing code that does one thing and does it well?

easy

A. Open/Closed Principle

B. Don't Repeat Yourself (DRY)

C. Single Responsibility Principle (SRP)

D. Keep It Simple, Stupid (KISS)

Solution

1. Step 1: Understand the principle names

   SRP means each module or class should have one responsibility or reason to change.

2. Step 2: Match the description to the principle

   Writing code that does one thing well matches SRP.

3. Final Answer:

   Single Responsibility Principle (SRP) -> Option C

4. Quick Check:

   One responsibility = SRP [OK]

Hint: One job per module means SRP [OK]

Common Mistakes:

• Confusing SRP with DRY which avoids repetition
• Thinking KISS means single responsibility
• Mixing Open/Closed with SRP

2. Which of the following is the correct description of the DRY principle?

easy

A. Avoid duplicating code or logic in multiple places

B. Keep code as simple as possible

C. Design software to be open for extension but closed for modification

D. Each class should have only one reason to change

Solution

1. Step 1: Recall DRY meaning

   DRY stands for "Don't Repeat Yourself", meaning avoid code duplication.

2. Step 2: Match option to DRY

   Avoid duplicating code or logic in multiple places says avoid duplicating code or logic, which matches DRY.

3. Final Answer:

   Avoid duplicating code or logic in multiple places -> Option A

4. Quick Check:

   DRY = no repetition [OK]

Hint: DRY means no repeated code [OK]

Common Mistakes:

• Confusing DRY with Open/Closed principle
• Mixing DRY with KISS which is about simplicity
• Thinking DRY means single responsibility

3. Consider this code snippet applying the KISS principle:

def calculate_area(radius):
    return 3.14 * radius * radius

area = calculate_area(5)
print(area)

What will be the output?

medium

A. 31.4

B. 78.5

C. Error due to missing import

D. None

Solution

1. Step 1: Calculate area using formula

   Area = π * radius² = 3.14 * 5 * 5 = 3.14 * 25 = 78.5

2. Step 2: Check code output

   The function returns 78.5 and print outputs it.

3. Final Answer:

   78.5 -> Option B

4. Quick Check:

   3.14 * 25 = 78.5 [OK]

Hint: Multiply π by radius squared for area [OK]

Common Mistakes:

• Using 2 * π * r (circumference) instead of area formula
• Expecting error due to missing math module (not needed here)
• Confusing output with None from missing return

4. Identify the error in this code violating the Open/Closed Principle:

class Shape:
    def area(self, shape_type, size):
        if shape_type == 'circle':
            return 3.14 * size * size
        elif shape_type == 'square':
            return size * size
        else:
            return 0

medium

A. The class is closed for modification

B. The method is open for extension without changes

C. The code uses inheritance properly

D. The area method uses conditional logic to handle multiple shapes

Solution

1. Step 1: Understand Open/Closed Principle

   It says software entities should be open for extension but closed for modification.

2. Step 2: Analyze the area method

   The method uses if-else to handle different shapes, so adding a new shape requires modifying this method.

3. Final Answer:

   The area method uses conditional logic to handle multiple shapes -> Option D

4. Quick Check:

   Conditional logic breaks Open/Closed [OK]

Hint: If-else for types breaks Open/Closed [OK]

Common Mistakes:

• Thinking inheritance is used properly here
• Believing the class is closed for modification
• Confusing open for extension with modifying code

5. You want to refactor this code to follow the Single Responsibility Principle (SRP):

class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email
    def save_to_database(self):
        # code to save user data
        pass
    def send_welcome_email(self):
        # code to send email
        pass

What is the best way to apply SRP here?

hard

A. Move save_to_database to a separate DatabaseHandler class

B. Keep all methods in User class since they relate to user

C. Combine both methods into one method for simplicity

D. Remove send_welcome_email method entirely

Solution

1. Step 1: Understand SRP

   SRP says a class should have only one reason to change, so User should only hold user data.

2. Step 2: Identify responsibilities

   Saving to database and sending emails are separate concerns from user data storage.

3. Step 3: Refactor accordingly

   Move save_to_database to a DatabaseHandler class to separate concerns.

4. Final Answer:

   Move save_to_database to a separate DatabaseHandler class -> Option A

5. Quick Check:

   Separate responsibilities = SRP applied [OK]

Hint: One class, one reason to change means separate concerns [OK]

Common Mistakes:

• Keeping all methods in one class breaks SRP
• Combining methods increases complexity
• Removing functionality instead of refactoring