Python Lists

A List is an ordered, mutable collection that can store items of any data type. Lists are one of Python's most powerful and frequently used data structures.

Why Lists Matter

Lists solve a fundamental programming problem: storing multiple related values. Instead of creating separate variables for each item, you can group them together.

# ❌ Without lists (tedious!)
fruit1 = "apple"
fruit2 = "banana"
fruit3 = "cherry"

# ✅ With lists (elegant!)
fruits = ["apple", "banana", "cherry"]

Creating Lists

Lists are created using square brackets [] with items separated by commas.

Understanding Indexing

Python uses zero-based indexing, meaning the first item is at index 0.

Slicing Lists

Slicing extracts a portion of a list using the syntax [start:end:step].

Modifying Lists (Mutability)

Unlike strings and tuples, lists are mutable - you can change their content after creation.

Adding Items to Lists

Python provides multiple methods to add items to lists.

Removing Items from Lists

Searching and Counting

Sorting and Reversing

List Operations

List Copying: Reference vs Copy

Critical Concept: Assignment creates a reference, not a copy!

Nested Lists (2D Lists)

Lists can contain other lists, creating multi-dimensional structures.

Lists as Stacks and Queues

Stack (LIFO - Last In, First Out)

Queue (FIFO - First In, First Out)

Common List Patterns

Coding Challenge: Shopping Cart 🛒

Build a simple shopping cart system.

Quiz

Key Takeaways

✅ Lists are ordered, mutable collections created with [].
✅ Use zero-based indexing to access items (first item is index 0).
✅ Slicing [start:end:step] extracts portions of lists.
✅ append() adds one item, extend() adds multiple items.
✅ Watch out for references! Use .copy() or [:] for true copies.
✅ Lists can be used as stacks (LIFO) or queues (FIFO).

What's Next?

In the next lesson, we'll explore Tuples - the immutable cousin of lists that offers performance benefits and data protection.

Keep coding! 🚀