Store, Repeat, Automate

🧭 Introduction

In the previous lesson, you learned how to use variables to store single values.
But in real life, we deal with lists of things: shopping items, tasks, names, scores.
And to process multiple items efficiently, we use lists and loops.

In this lesson you’ll learn how to:

• Create and modify lists
• Use loops to process items automatically
• Build a simple interactive To-Do List app

📦 1. Lists in Python

✅ Basic Example

shopping = ["Milk", "Bread", "Eggs", "Water"]
print(shopping)

💬 Output:

['Milk', 'Bread', 'Eggs', 'Water']

A list is an ordered, editable container that holds multiple values.

🔍 Access by Index

print(shopping[0])   # First item
print(shopping[2])   # Third item
print(shopping[-1])  # Last item

💬 Output:

Milk
Eggs
Water

Indexes start at 0. Negative indexes count from the end.

🧠 2. Modifying a List

➕ Add Items

shopping.append("Cookies")
print(shopping)

💬 Output:

['Milk', 'Bread', 'Eggs', 'Water', 'Cookies']

➖ Remove Items

shopping.remove("Bread")
print(shopping)

💬 Output:

['Milk', 'Eggs', 'Water', 'Cookies']

🧨 Pop the Last Item

last = shopping.pop()
print("Removed:", last)
print(shopping)

💬 Output:

Removed: Cookies
['Milk', 'Eggs', 'Water']

🧮 Count Items

print("You have", len(shopping), "items.")

💬 Output:

You have 3 items.

🔁 3. Loops: Process Each Item Automatically

🧪 Basic Loop

for item in shopping:
    print("✔️", item)

💬 Output:

✔️ Milk
✔️ Eggs
✔️ Water

🔢 Enumerate with Index

for i, item in enumerate(shopping, start=1):
    print(f"{i}) {item}")

💬 Output:

1) Milk
2) Eggs
3) Water

🧰 4. Mini App — Interactive To-Do List

🎯 Goal:

Create an interactive program that builds a to-do list from user input.

💻 Code:

todo = []

print("Welcome! Enter your tasks. Type 'done' to finish.")

while True:
    task = input("New task: ")
    if task.lower() == "done":
        break
    todo.append(task)

print("\n📋 Your To-Do List:")
for i, task in enumerate(todo, start=1):
    print(f"{i}. {task}")

💬 Example Output:

Welcome! Enter your tasks. Type 'done' to finish.
New task: Study Python
New task: Buy milk
New task: Gym
New task: done

📋 Your To-Do List:
1. Study Python
2. Buy milk
3. Gym

🧪 5. Practice Challenge — Average & Maximum

🧠 Description:

Write a program that:

• Asks the user for 5 numbers
• Saves them in a list
• Prints the average and maximum value

💻 Code:

numbers = []

for i in range(5):
    n = float(input(f"Enter number {i+1}: "))
    numbers.append(n)

average = sum(numbers) / len(numbers)
maximum = max(numbers)

print("\nNumbers:", numbers)
print("Average:", average)
print("Maximum:", maximum)

💬 Sample Output:

Enter number 1: 10
Enter number 2: 7.5
Enter number 3: 9
Enter number 4: 4
Enter number 5: 12

Numbers: [10.0, 7.5, 9.0, 4.0, 12.0]
Average: 8.5
Maximum: 12.0

🎯 What You Learned

• How to use lists to store multiple values
• How to loop through lists using for and enumerate
• How to build real programs that interact with the user