Core Data Structures in Python

Core Data Structures in Python

Python provides several built-in collection types that are used to store, organize, and manipulate data efficiently.
These data structures are flexible and map closely to collections in C# and JavaScript.

1. List

nums = [1, 2, 3]

What is a List?

A list is:

• Ordered collection
• Mutable (can be changed)
• Can store duplicate values
• Can store mixed data types

Key Characteristics

• Maintains insertion order
• Elements can be added, removed, or modified
• Index-based access

nums.append(4)
nums[0] = 10

C# Equivalent

List<int> nums = new List<int> { 1, 2, 3 };

JavaScript Equivalent

const nums = [1, 2, 3];

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2. Tuple

point = (4, 5)

What is a Tuple?

A tuple is:

• Ordered collection
• Immutable (cannot be changed)
• Typically used for fixed collections of values

Key Characteristics

• Faster than lists
• Often used for coordinates, pairs, and return values
• Safer when data should not change

x, y = point  # tuple unpacking

C# Equivalent

(int x, int y) point = (4, 5);

JavaScript Equivalent

JavaScript does not have tuples natively, but arrays are used:

const point = [4, 5];

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3. Dictionary (dict)

user = {"name": "Ada"}

What is a Dictionary?

A dictionary:

• Stores key–value pairs
• Keys must be unique
• Values can be of any type
• Mutable

Key Characteristics

• Fast lookups by key
• Insertion order preserved (Python 3.7+)

user["age"] = 30

C# Equivalent

Dictionary<string, string> user = new Dictionary<string, string>
{
    { "name", "Ada" }
};

JavaScript Equivalent

const user = { name: "Ada" };

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4. Set

unique = {1, 2, 2, 3}

What is a Set?

A set is:

• Unordered collection
• Stores unique values only
• Automatically removes duplicates

Result:

{1, 2, 3}

Key Characteristics

• No indexing
• Extremely fast membership checks
• Useful for removing duplicates and set operations

2 in unique  # True

C# Equivalent

HashSet<int> unique = new HashSet<int> { 1, 2, 2, 3 };

JavaScript Equivalent

const unique = new Set([1, 2, 2, 3]);

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5. Summary Table

Python Type	Ordered	Mutable	Allows Duplicates	C# Equivalent	JavaScript Equivalent
list	✅	✅	✅	List<T>	Array
tuple	✅	❌	✅	(T1, T2)	Array
dict	✅	✅	❌ (keys)	Dictionary<TKey, TValue>	Object
set	❌	✅	❌	HashSet<T>	Set

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6. When to Use What

• List → Ordered, changeable collections
• Tuple → Fixed, read-only groupings
• Dictionary → Key-value relationships
• Set → Unique values and fast membership checks

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7. Final Summary

• Python’s core data structures are powerful and flexible
• They closely map to familiar C# and JavaScript collections
• Choosing the right structure improves performance and readability
• Understanding mutability and ordering is critical