Module 2 Lesson 6: Choosing the Right Data Structure

Now you know how to use Lists, Tuples, Dictionaries, and Sets. But in the real world, the hardest part isn't writing the code—it's choosing the right tool for the job. Picking the wrong structure can make your code slow, confusing, or buggy.

Lesson Overview

In this lesson, we will cover:

• The Cheat Sheet: A quick comparison table.
• Real-world Scenarios: matching problems to solutions.
• The Decision Flowchart: How a pro thinks about data.
• Performance vs. Readability: Finding the balance.

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1. The Comparison Matrix

Structure	Ordered?	Changeable?	Unique?	Access By
List []	Yes	Yes	No	Index (Position)
Tuple ()	Yes	No	No	Index (Position)
Dict {}	Yes*	Yes	Keys (Yes)	Key (Label)
Set {}	No	Yes	Yes	Value (Member)

*Note: In modern Python, Dictionaries remember the order in which items were added.

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2. Choosing by Scenario

Scenario A: A Shopping Cart

• Requirement: Items need to stay in order, and you might add or remove them.
• Winner: List.

Scenario B: Student IDs

• Requirement: You have 10,000 IDs and need to know INSTANTLY if an ID is valid or not. You don't want duplicates.
• Winner: Set.

Scenario C: Fixed GPS Coordinates

• Requirement: A location is always (Lat, Lon). You don't want anyone accidentally changing just the longitude.
• Winner: Tuple.

Scenario D: User Profiles

• Requirement: You need to store many details (name, age, email) and look them up by their labels.
• Winner: Dictionary.

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3. The Decision Flowchart

When you have data, ask yourself these questions in order:

1. Do I need Key-Value pairs?
   • Yes → Dictionary
2. Does it need to be unique?
   • Yes → Set
3. Should it be unchangeable?
   • Yes → Tuple
4. None of the above?
   • Use a List.

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4. Performance: The "Big O" Preview

As your data grows from 10 items to 10 million, the differences become huge.

• In a List: To see if item X exists, Python has to check every item (Slow).
• In a Set or Dictionary: Python uses a "Hash Map" to jump directly to the item (Lightning Fast).

Always use a Set or Dict for massive search operations!

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Practice Exercise: The Architect

For each of these data sets, identify the best Python data structure and write a one-line code example:

1. The names of the months in a year.
2. The friends on your social media "Followers" list.
3. A collection of book titles and their authors.
4. A list of the last 5 websites you visited (browser history).

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Quick Knowledge Check

1. Why is a Set faster than a List for searching?
2. Which structure is best for grouping related details about a single object?
3. When should you use a Tuple instead of a List?
4. If you need to store items in a specific order and might have duplicates, what do you use?

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Key Takeaways

• Dictionaries are for labeled data.
• Sets are for unique, fast-search data.
• Tuples are for safe, constant data.
• Lists are the default for everything else.

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What’s Next?

We’ve mastered the "What" (Data Structures). Now it’s time for the "How" (Algorithms). In Lesson 7, we’ll begin the second half of this module: Introduction to Algorithms!