Python Lists

🎯 Learning Objectives

By the end of this lesson, you will be able to:

• Understand what lists are and why we use them
• Create lists in different ways
• Access and modify items in a list
• Add and remove items from lists
• Use lists to solve real-world problems

ℹ️ Definition: A list is a data structure that stores a collection of items. Lists are ordered (items have positions) and changeable (you can modify them).

📚 Why Do We Need Lists?

• Variables store data while your program runs. But what if you need to store many similar items?
• Creating lots of separate variables takes up more memory and makes your code messy.
• For example, storing student names without lists would look like this:

student_1 = "Sharvin"
student_2 = "Yong"
student_3 = "Sheng"

This approach creates too many variables!

• Python solves this problem with lists. You can store all the names in one variable:

students = ["Sharvin", "Yong", "Sheng"]

Much cleaner with just one variable!

🔧 List Structure

Every list has three parts:

• List name: The variable that holds your list
• Square brackets [ ]: These contain your items
• Commas: These separate each item

🎨 Types of Data in Lists

Lists can store different types of data:

Data Type	Code Example	Output
Same Type	student = ["Sharvin", "Yong", "Sheng"]
Mixed Types	student_details = ["Sharvin", 20, "M"]

📝 Note Important: Every item in a list has an index (position number) starting from 0. The index tells you where to find each item.

🗂️ What You'll Learn

We'll explore five key list operations:

1. Create and Generate Lists - Making new lists
2. Access Items - Getting data from lists
3. Change Items - Modifying existing data
4. Add Items - Putting new data in lists
5. Remove Items - Taking data out of lists

🏗️ Create and Generate List

Method 1: Manual Creation

You can create a list by typing all the values:

numbers = [1,2,3,4,5,6,7,8,9,10,
          11,12,13,14,15,16,17,18,19,20]
print(numbers)

Expected output:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

Method 2: Using range() Function

Python provides a faster way using range() and list():

numbers = list(range(1,21))
print(numbers)

Expected output:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

💡 The ending number in range() is not included. This makes it easy to create lists with exact counts. For example, range(20) gives you exactly 20 numbers (0 to 19).

Creating Lists Starting from 0

python

numbers = list(range(20))
print(numbers)

Expected output:

csharp

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

---

Breaking Strings into Characters

The list() function can also split a string into individual characters:

python

chars = list("Hello, world")
print(chars)

Expected output:

css

['H', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd']

---

Creating Empty Lists

Sometimes you need to start with an empty list and add items later:

python

numbers = []
print(numbers)

Expected output:

css

[]

---

🔍 Access Items in List

Getting a Single Item

Use the index number in square brackets to get an item:

python

students = ["Sharvin", "Yong", "Sheng"]
print(students[0])

Expected output:

Sharvin

---

Negative Indexing

Python lets you count from the end using negative numbers:

python

students = ["Sharvin", "Yong", "Sheng"]
print(students[-1])

Expected output:

Sheng

---

Getting Multiple Items (Slicing)

You can get several items at once using slicing:

python

numbers = [1,4,8,2]
print(numbers[1:3])

Expected output:

csharp

[4, 8]

---

Finding an Item's Position

Use .index() to find where an item is located:

python

numbers = [1,4,8,2]
print(numbers.index(8))

Expected output:

2

---

Checking if an Item Exists

Use the in keyword to check if something is in your list:

python

numbers = [1,4,8,2]
print(4 in numbers)

Expected output:

graphql

True

---

✏️ Change Item in List

Changing an item is simple - just assign a new value to that position:

python

numbers = [1,4,8,2]
numbers[1] = 6
print(numbers)

Expected output:

csharp

[1, 6, 8, 2]

---

➕ Add Item in List

Method 1: append() - Add to the End

Use .append() to add an item at the end of your list:

python

numbers = [1,4,8,2]
numbers.append(3)
print(numbers)

Expected output:

csharp

[1, 4, 8, 2, 3]

---

Method 2: insert() - Add at a Specific Position

Use .insert() to add an item exactly where you want it:

python

numbers = [1,4,8,2]
numbers.insert(2,3)
print(numbers)

Expected output:

csharp

[1, 4, 3, 8, 2]

---

➖ Remove Item in List

Method 1: remove() - Remove by Value

Use .remove() when you know what item you want to delete:

python

numbers = [1,4,8,2]
numbers.remove(8)
print(numbers)

Expected output:

csharp

[1, 4, 2]

---

Method 2: del - Remove by Position

Use del when you know the index of the item to remove:

python

numbers = [1,4,8,2]
del numbers[1]
print(numbers)

Expected output:

csharp

[1, 8, 2]

📝 Summary

Lists are powerful tools in Python that help you:

• Store multiple items in one variable
• Access items using index numbers (starting from 0)
• Modify, add, and remove items as needed
• Work with different types of data together tip Remember: Lists are like containers that can hold many items. You can think of them as a row of boxes, where each box has a number (index) and contains one item.

🎥 Video

🤖 AI Prompt

Code with AI: Try using AI to generate code involving lists and conditional statements.

Prompts:

• "Write a Python program that checks if a number is even or odd."
• "Generate Python code to find the largest number in a list."

🏃 Practice Time!

Try these exercises to master lists:

1. Shopping List: Create a list of 5 items you need from the store. Then:

   • Add a new item using append()
   • Remove one item using remove()
   • Change the third item to something else

2. Number Explorer: Create a list of numbers from 1 to 10 using range(). Then:

   • Print the first number
   • Print the last number using negative indexing
   • Print numbers from position 2 to 5

3. Name Checker: Create a list of your friends' names. Then:

   • Check if "Alice" is in your list
   • Find the position of one friend's name
   • Add a new friend at position 2