Python Lists 🚀

Prerequisites: Python Variables, Python Loops

Mentor's Note: A list is like a multi-purpose container. It's the most flexible and commonly used way to store data in Python! 💡

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🌟 The Scenario: The Shopping Bag 🛍️

Imagine you are going to the market with a reusable shopping bag.

• The Logic:
  • You can put many items inside (Apple, Milk, Bread). 📦
  • The items are ordered (the Apple is at the bottom, the Bread is on top). 🔢
  • You can change the items (swap the Milk for Juice). 🔄
  • You can have duplicates (you can buy two Apples). 🍎🍎
• The Result: A flexible collection of items that you can manage easily. ✅

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📖 Concept Explanation

1. What is a List?

A list is a collection which is ordered and changeable. It allows duplicate members.

2. Creating & Accessing

Lists are written with square brackets [].

fruits = ["Apple", "Banana", "Cherry"]
print(fruits[0]) # Output: Apple (Index starts at 0!)

3. Changeable (Mutable)

Unlike Strings, you can change a specific item in a list:

fruits[1] = "Mango" # Banana is now replaced! 🥭

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🎨 Visual Logic: List Anatomy

graph LR
    subgraph List: ["fruits"]
    A[0: Apple] --- B[1: Banana]
    B --- C[2: Cherry]
    end
    D[New Item] -- .append --> C

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💻 Implementation: The List Lab

Python (3.10+)

# 🛒 Scenario: Managing a Task List
# 🚀 Action: Adding, removing, and sorting tasks

tasks = ["Code", "Eat", "Sleep"]

# 1. Add a new task ➕
tasks.append("Review")

# 2. Insert at a specific spot 📍
tasks.insert(1, "Fix Bug")

# 3. Remove the last completed task ❌
done = tasks.pop() # Removes "Review"

# 4. Sort alphabetically 🔡
tasks.sort()

print(f"Remaining tasks: {tasks}")
# 🛍️ Outcome: ["Code", "Eat", "Fix Bug", "Sleep"] (sorted)

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📊 Sample Dry Run (Methods)

Initial List: L = [10, 20]

Instruction	List State	Description
L.append(30)	[10, 20, 30]	30 added to end 📥
L.pop(0)	[20, 30]	Item at index 0 (10) removed 📤
L.extend([40, 50])	[20, 30, 40, 50]	Multiple items added 🛍️

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📉 Complexity Analysis

• Accessing by Index: \(O(1)\) - Instant! ⚡
• Adding to End (append): \(O(1)\) - Very fast.
• Inserting/Deleting at Start: \(O(n)\) - Slow (Python has to shift all other items).

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🎯 Practice Lab 🧪

Task: The Guest List

Task: Create a list of 3 friends. Add a new friend to the beginning of the list using insert(). Then, print the total number of guests using len(). Hint: insert(0, "Name"). 💡

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← Back: Control Flow | Next: Tuples →

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