DRY (Don't Repeat Yourself) in Software Engineering - Mini Project: Build & Apply

Understanding DRY (Don't Repeat Yourself) Principle

📖 Scenario: You are working on a small project where you need to calculate the area of different shapes multiple times. To keep your code clean and avoid repeating the same calculations, you will learn how to apply the DRY principle.

🎯 Goal: Build a simple example that shows how to avoid repeating code by using a function to calculate areas of shapes.

📋 What You'll Learn

Create variables with shape dimensions

Create a helper variable for shape type

Write a function to calculate area based on shape type

Use the function to get area without repeating code

💡 Why This Matters

🌍 Real World

In real projects, avoiding repeated code saves time and reduces errors when making changes.

💼 Career

Understanding DRY is essential for writing clean, maintainable code in any software development role.

1

DATA SETUP: Define shape dimensions

Create two variables called length and width with values 5 and 3 respectively.

Software Engineering

# Create variables length and width with values 5 and 3
# Your code here

Hint

Use simple assignment statements like length = 5.

2

CONFIGURATION: Define the shape type

Create a variable called shape and set it to the string "rectangle".

Software Engineering

length = 5
width = 3
# Create a variable shape and set it to "rectangle"
# Your code here

Hint

Assign the string "rectangle" to the variable shape.

3

CORE LOGIC: Write a function to calculate area

Define a function called calculate_area that takes shape, length, and width as parameters. Inside the function, use an if statement to return length * width if shape is "rectangle". Otherwise, return 0.

Software Engineering

length = 5
width = 3
shape = "rectangle"
# Define function calculate_area(shape, length, width) with if statement
# Your code here

Hint

Use a function with parameters and an if-else statement to decide the area.

4

COMPLETION: Use the function to get the area

Create a variable called area and set it to the result of calling calculate_area with shape, length, and width as arguments.

Software Engineering

length = 5
width = 3
shape = "rectangle"
def calculate_area(shape, length, width):
    if shape == "rectangle":
        return length * width
    else:
        return 0
# Call calculate_area and assign result to area
# Your code here

Hint

Call the function with the variables and assign the result to area.

Practice

1. What does the DRY principle in software engineering mean?

easy

A. Don't Repeat Yourself - avoid writing the same code multiple times

B. Debug Regularly Yourself - test code often

C. Develop Rapidly Yesterday - finish tasks quickly

D. Design Reusable Yields - focus on output

Solution

1. Step 1: Understand the acronym DRY

   DRY stands for "Don't Repeat Yourself" which means avoiding duplicate code.

2. Step 2: Match the meaning to options

   Don't Repeat Yourself - avoid writing the same code multiple times correctly explains DRY as avoiding repeated code to keep it clean and maintainable.

3. Final Answer:

   Don't Repeat Yourself - avoid writing the same code multiple times -> Option A

4. Quick Check:

   DRY = Don't Repeat Yourself [OK]

Hint: DRY means write code once, reuse it everywhere [OK]

Common Mistakes:

• Confusing DRY with debugging or speed
• Thinking DRY means writing less code overall
• Assuming DRY is about output or design only

2. Which of the following is the correct way to apply DRY in code?

easy

A. Use functions or methods to reuse code

B. Copy and paste the same code block multiple times

C. Write all code in one long script without breaks

D. Repeat variable declarations for clarity

Solution

1. Step 1: Identify how to avoid code repetition

   Functions or methods allow reusing code by calling them multiple times instead of copying code.

2. Step 2: Compare options for DRY compliance

   Use functions or methods to reuse code uses functions to reuse code, which follows DRY. Others increase repetition.

3. Final Answer:

   Use functions or methods to reuse code -> Option A

4. Quick Check:

   Functions help reuse code [OK]

Hint: Functions help avoid repeating code [OK]

Common Mistakes:

• Copy-pasting code instead of using functions
• Writing long scripts without modular parts
• Repeating declarations unnecessarily

3. Consider this code snippet:

def greet():
    print('Hello!')

greet()
greet()

What is the main benefit of using the function greet() here?

medium

A. It causes a syntax error

B. It repeats the print statement twice

C. It makes the program slower

D. It avoids repeating the print code by calling the function

Solution

1. Step 1: Analyze the function usage

   The function greet() contains the print statement and is called twice.

2. Step 2: Understand the benefit

   Instead of writing print('Hello!') twice, the function is called twice, avoiding code repetition.

3. Final Answer:

   It avoids repeating the print code by calling the function -> Option D

4. Quick Check:

   Function calls reuse code [OK]

Hint: Functions let you write code once, run many times [OK]

Common Mistakes:

• Thinking function calls duplicate code
• Assuming functions slow down simple prints
• Believing this causes syntax errors

4. Identify the problem in this code snippet related to DRY:

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

print(calculate_area(5))
print(3.14 * 7 * 7)

medium

A. The value of pi is incorrect

B. The function is not called for the second print, repeating code

C. The function has a syntax error

D. The function returns nothing

Solution

1. Step 1: Check code repetition

   The first print uses the function, but the second print repeats the area calculation manually.

2. Step 2: Identify DRY violation

   Repeating the formula outside the function breaks DRY; both should use the function.

3. Final Answer:

   The function is not called for the second print, repeating code -> Option B

4. Quick Check:

   Repeated formula outside function breaks DRY [OK]

Hint: Always reuse functions instead of repeating formulas [OK]

Common Mistakes:

• Ignoring repeated formula outside function
• Thinking the function has syntax errors
• Assuming pi value causes DRY issues

5. You have a list of prices and want to apply a 10% discount to each without repeating code. Which approach best follows the DRY principle?

hard

A. Write a loop that calculates discounted price inside the loop body each time

B. Manually calculate discount for each price separately

C. Create a function to calculate discount and call it for each price

D. Copy the discount calculation code multiple times in the program

Solution

1. Step 1: Understand the task

   Applying the same discount calculation repeatedly should be done without copying code.

2. Step 2: Choose the DRY-compliant method

   Creating a function for discount calculation and calling it for each price avoids repetition and keeps code clean.

3. Final Answer:

   Create a function to calculate discount and call it for each price -> Option C

4. Quick Check:

   Functions prevent repeated discount code [OK]

Hint: Use functions to apply repeated calculations [OK]

Common Mistakes:

• Repeating calculation code in loops or manually
• Copy-pasting discount logic multiple times
• Not using reusable code blocks