Debugging Techniques for Beginners: Find and Fix Bugs Step-by-Step

Every developer writes bugs.

Even senior engineers with 10+ years of experience introduce errors. The real difference between beginners and professionals is not “who writes fewer bugs” — it’s:

Who can debug faster, calmer, and more methodically?

If you’ve ever:

• Stared at an error message without understanding it
• Changed random lines hoping something would work
• Fixed one bug and created two new ones
• Felt frustrated because “it should work”

This guide is for you.

You’ll learn:

• A systematic debugging mindset
• Practical techniques (print, logs, breakpoints, isolation)
• How to read error messages properly
• How to avoid making debugging worse
• Exercises with real buggy examples

This is part of the Programming Best Practices cluster and will dramatically improve your troubleshooting skills.

🔹 Key Takeaways

🔹 Quick Navigation

🐞 What Is Debugging?

Debugging is the process of:

• Identifying
• Isolating
• Understanding
• Fixing

an error in your program.

A “bug” is simply behavior that is:

• Incorrect
• Unexpected
• Crashing
• Slower than intended

Debugging is a skill.
And like any skill, it improves with practice and structure.

🧠 The Debugging Mindset

When your code breaks, your first reaction matters.

Bad mindset:

• “This makes no sense”
• “I’ll just change random things”
• “Maybe restarting will fix it”

Good mindset:

• “What exactly is happening?”
• “Where does it fail?”
• “What changed recently?”

Core Rule

Never guess. Always gather evidence.

🧭 The 7-Step Professional Debugging Framework

Professional developers rarely debug randomly. They follow a structured method.

Here is a practical 7-step framework you can apply immediately:

This workflow alone can dramatically improve your debugging speed.

🏗️ Real-World Debugging Scenario

Let’s simulate a common beginner situation.

Your API should return a user’s age category, but it behaves incorrectly.

def age_category(age):
    if age > 18:
        return "Adult"
    elif age > 13:
        return "Teen"
    else:
        return "Child"

print(age_category(15))

Expected output:

Teen

Actual output:

Adult

🔍 Why is this happening?

The first condition checks if age > 18.

But 15 is not greater than 18 — so that’s fine.

Wait… look carefully.

The logical mistake is subtle: the order of conditions can affect logic in many real cases.

Now imagine a different mistake:

def age_category(age):
    if age > 13:
        return "Teen"
    elif age > 18:
        return "Adult"
    else:
        return "Child"

Now every adult will be categorized as “Teen”.

This is a logic error, not a syntax error.

Debugging logic errors requires reading the code slowly and reasoning step by step.

⚡ Debugging Performance Issues

Not all bugs crash your program. Some bugs make it slow.

def slow_function():
    result = []
    for i in range(1000000):
        result.append(i)
    return result

This might work — but what if it runs inside another loop?

Performance debugging involves:

• Measuring execution time
• Finding repeated work
• Reducing unnecessary loops
• Using built-in optimized functions

Improved version:

def faster_function():
    return list(range(1000000))

Cleaner and faster.

🧪 Logging vs Printing

Print debugging is useful, but logging is more powerful.

import logging

logging.basicConfig(level=logging.INFO)

logging.info("Application started")

🧠 Always Test Edge Cases

Edge cases are inputs at the limits of your logic.

Examples:

• Empty lists
• Very large numbers
• Negative values
• Null or None

Professional developers test edge cases before deploying code.

🚀 How to Improve Debugging Skills Long-Term

Debugging improves with experience, but you can accelerate learning:

• Read other people’s code
• Fix open-source beginner issues
• Practice code challenges intentionally breaking logic
• Review your own old code and refactor it
• Write unit tests to catch bugs early

The best developers are not those who avoid bugs.

They are those who can diagnose them quickly and calmly.

📂 Types of Bugs

🔍 How to Read Error Messages

Most beginners ignore error messages.

That’s a mistake.

Example:

def divide(a, b):
    return a / b

print(divide(10, 0))

Error:

ZeroDivisionError: division by zero

This tells you:

• File
• Line
• Type of error
• Exact issue

Always read:

1. Error type
2. Message
3. Line number
4. Call stack

🖨️ Print Debugging

The simplest technique: print variables.

Example:

def calculate_discount(price):
    print("Price received:", price)
    if price > 100:
        return price * 0.1
    return 0

This helps answer:

• Is function being called?
• What value is passed?

Print debugging is simple but powerful.

⏸️ Using Breakpoints

Modern IDEs allow breakpoints.

What they do:

• Pause execution
• Let you inspect variables
• Step line by line

Breakpoints are better than printing when:

• Complex logic
• Multiple function calls
• Hard-to-track state changes

🧩 Divide and Conquer Strategy

If your app has 500 lines and something breaks:

Do NOT debug 500 lines at once.

Instead:

1. Identify where failure starts
2. Comment out half the code
3. Test smaller parts

This method quickly narrows down the problem.

🦆 Rubber Duck Debugging

Explain your code out loud.

Seriously.

When you explain step-by-step:

• You often discover logical mistakes.
• Your brain catches inconsistencies.

You don’t even need a real duck. Just pretend.

📊 Debugging Strategy Table

🧪 Debugging Mini Project

Try It Yourself

This code should calculate average:

def average(numbers):
    total = 0
    for n in numbers:
        total += n
    return total / len(numbers)

print(average([]))

What’s wrong?

def average(numbers):
    if len(numbers) == 0:
        raise ValueError("List cannot be empty")
    total = sum(numbers)
    return total / len(numbers)

⚠️ Common Debugging Mistakes

✅ Debugging Checklist

🧠 Mini Quiz

❓ FAQ

📚 Recommended Reading

• Clean Code Guide: Write Better, Safer, and Easier-to-Maintain Code
• REST API Tutorial: Build and Use Your First API Step-by-Step
• AI Web App: Build a Beginner-Friendly Prediction App Step-by-Step (Python + FastAPI)
• Deploying Your First App to AWS: A Beginner-Friendly Step-by-Step Tutorial