Introduction to Python Collections

In Python, collections are ways to store multiple values in a single variable. Imagine a box where you can keep many items together – that’s what collections help you do in programming.

Python has four main types of collections:

• List – an ordered, changeable collection
• Tuple – an ordered, unchangeable collection
• Set – an unordered, unique collection
• Dictionary – a collection of key-value pairs

1. List – A Changeable Ordered Collection

Lists let you store multiple items in one variable. You can change, add, or remove items.

fruits = ["apple", "banana", "cherry"]
print(fruits)

['apple', 'banana', 'cherry']

Why this output? The list keeps all three fruits in the order they were added. The square brackets [] show it’s a list.

2. Tuple – A Fixed Ordered Collection

Tuples are like lists, but you can’t change them once created.

colors = ("red", "green", "blue")
print(colors)

('red', 'green', 'blue')

Why this output? The items are inside parentheses (), showing it’s a tuple. The order is kept, but the values can’t be changed later.

3. Set – A Unique Unordered Collection

Sets store items without any duplicates and without keeping order.

numbers = {1, 2, 3, 2, 1}
print(numbers)

{1, 2, 3}

Why this output? Sets remove duplicates automatically. The numbers 2 and 1 appeared twice but are shown only once. The order may vary each time you run the code.

4. Dictionary – A Collection of Key-Value Pairs

Dictionaries store data in a key: value format. Each key is unique and helps you find its value.

student = {"name": "Alice", "age": 20}
print(student)

{'name': 'Alice', 'age': 20}

Why this output? The dictionary keeps two key-value pairs. The keys "name" and "age" point to their respective values.

Summary Table – Comparing Python Collections

Type	Ordered?	Changeable?	Duplicates Allowed?	Syntax
List	Yes	Yes	Yes	[ ]
Tuple	Yes	No	Yes	( )
Set	No	Yes	No	{ }
Dictionary	No (but keys are read in insertion order)	Yes	No (keys must be unique)	{ key: value }

When to Use Each?

• Use a list when you need a collection that can change and has a specific order (e.g., a shopping list).
• Use a tuple when the collection should never change (e.g., fixed coordinates).
• Use a set when you only care about unique items (e.g., all unique tags from a blog).
• Use a dictionary when you need to pair data (e.g., a person's name and age).

What’s Next?

In the upcoming lessons, we’ll explore each of these collection types in more detail, with more examples, tricks, and real-life uses. 🎯