Lesson 07 – Python Lists: Create, Access, Change, Add & Remove

Lesson Introduction

Imagine you are keeping track of your five favourite fruits. You could store each one in a separate variable:

fruit1 = "apple"
fruit2 = "banana"
fruit3 = "cherry"
fruit4 = "mango"
fruit5 = "grape"

That works — but what if you had 500 fruits? Or what if the number of fruits changes every day? Creating 500 individual variables would be a nightmare.

Python solves this with a list — a single container that can hold as many items as you need, all under one name. Lists are one of the most important and most-used tools in all of Python. You will use them in data analysis, web development, automation, science, games, finance, and almost every real-world Python project.

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

  • Create lists and understand exactly what they are
  • Access any item in a list using its index number
  • Change items that are already in a list
  • Add new items to a list
  • Remove items from a list
  • Build a working mini-project that uses all five skills together

Prerequisite Concepts

Before we start, here are the small things you need to already know. If any of these feel unfamiliar, re-read your earlier lessons first.

Concept Quick reminder
Variables name = "Alice" — a labelled box that stores a value
print() Displays output to the screen
Data types str (text), int (whole number), float (decimal), bool (True/False)
len() Counts how many characters are in a string — we will use it to count list items today

No other prior knowledge is needed. Everything else is taught from scratch right here.

Part 1 – What Is a Python List?

1.1 The Real-World Analogy

Think of a shopping list on paper:

1. Milk
2. Eggs
3. Bread
4. Butter

Each item has a position (1st, 2nd, 3rd, 4th).
You can add a new item at the bottom.
You can cross off (remove) something you already bought.
You can change “Butter” to “Olive Oil”.

A Python list works in exactly the same way — except it lives inside your program.

1.2 The Technical Definition

A Python list is:

  • An ordered collection of items (items always stay in the order you put them, unless you change that order)
  • Changeable (you can add, remove, and edit items after creating the list)
  • Allows duplicates (the same value can appear more than once)
  • Written with square brackets [] and items separated by commas ,

1.3 Creating Your First List

Syntax:

list_name = [item1, item2, item3]

Simple Example 1 – A list of fruits (strings):

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

Expected output:

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

What happened? Python stored three text values inside one variable called fruits. Notice the square brackets and the commas.

Simple Example 2 – A list of numbers:

scores = [95, 87, 76, 100, 60]
print(scores)

Expected output:

[95, 87, 76, 100, 60]

Simple Example 3 – A list of mixed data types:

Python lists can hold different types in the same list:

mixed = ["Alice", 25, True, 3.14]
print(mixed)

Expected output:

['Alice', 25, True, 3.14]

Thinking prompt: Why would storing different types together be useful? Imagine a student record: name (string), age (int), passed (bool), GPA (float).

1.4 How Many Items? — len()

The built-in len() function counts the number of items in a list.

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

Expected output:

3

1.5 Lists Can Hold Other Lists (Nested Lists)

A list can even contain another list inside it. This is called a nested list.

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
print(matrix)

Expected output:

[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

We will not go deep into nested lists today, but it is important you know they exist.

1.6 The list() Constructor

You can also create a list using the list() function:

colours = list(("red", "green", "blue"))
print(colours)

Expected output:

['red', 'green', 'blue']

Note: Notice the double parentheses (( )) — the inner () creates a tuple (another collection type), and list() converts it into a list.

1.7 List Data Type

To confirm something is a list, use type():

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

Expected output:

<class 'list'>

Part 2 – Accessing List Items

2.1 What Is an Index?

Every item in a list has a position number called an index.

Analogy: Think of seats in a cinema row. Seat 0 is the first seat, seat 1 is the second, and so on.

Python indexes start at 0, not 1. This is called zero-based indexing and is used in almost all programming languages.

List:   ["apple", "banana", "cherry", "mango", "grape"]
Index:      0         1         2        3        4

2.2 Accessing a Single Item

Use the list name followed by the index number inside square brackets:

fruits = ["apple", "banana", "cherry"]
print(fruits[0])   # First item
print(fruits[1])   # Second item
print(fruits[2])   # Third item

Expected output:

apple
banana
cherry

Common beginner mistake: Trying fruits[3] when only 3 items exist (indexes 0, 1, 2). This causes an IndexError: list index out of range.

Corrected version:

fruits = ["apple", "banana", "cherry"]
print(len(fruits))     # 3 items → valid indexes are 0, 1, 2
print(fruits[2])       # Correct: last item
# print(fruits[3])     # WRONG: would crash

2.3 Negative Indexing

Python also allows negative indexes. A negative index counts from the end of the list.

List:   ["apple", "banana", "cherry"]
Neg:       -3        -2        -1

-1 is always the last item. -2 is second from last. And so on.

fruits = ["apple", "banana", "cherry"]
print(fruits[-1])   # Last item
print(fruits[-2])   # Second from last
print(fruits[-3])   # Third from last (same as index 0)

Expected output:

cherry
banana
apple

Thinking prompt: When would negative indexing be more useful than positive indexing? Hint: when you always want the last few items, regardless of list length.

2.4 Range of Indexes (Slicing)

You can grab a slice (a section) of a list using a colon : inside the brackets.

Syntax:

list_name[start : end]
  • start = the index to begin from (included)
  • end = the index to stop before (NOT included)
fruits = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(fruits[2:5])

Expected output:

['cherry', 'orange', 'kiwi']

Items at indexes 2, 3, and 4 are returned. Index 5 is the stopping point — it is NOT included.

Leaving out the start index — slice from the beginning:

fruits = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(fruits[:4])

Expected output:

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

Leaving out the end index — slice to the end:

fruits = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(fruits[2:])

Expected output:

['cherry', 'orange', 'kiwi', 'melon', 'mango']

Negative index slicing:

fruits = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(fruits[-4:-1])

Expected output:

['orange', 'kiwi', 'melon']

2.5 Checking If an Item Exists — in Keyword

Use the in keyword to check whether a specific value is present in the list:

fruits = ["apple", "banana", "cherry"]

if "banana" in fruits:
    print("Yes, banana is in the list!")

Expected output:

Yes, banana is in the list!

if "mango" in fruits:
    print("Found mango")
else:
    print("mango is NOT in the list")

Expected output:

mango is NOT in the list

Part 3 – Changing List Items

3.1 Why Would You Change a List Item?

Lists are mutable — meaning you can change their contents after creation. This is different from strings, which are immutable (once created, you cannot change individual characters).

Real-world example: A store’s inventory changes daily. Items go in and out of stock. A list lets you update that data without rebuilding everything from scratch.

3.2 Changing One Item

Assign a new value directly to a specific index:

fruits = ["apple", "banana", "cherry"]
fruits[1] = "mango"
print(fruits)

Expected output:

['apple', 'mango', 'cherry']

Position 1 (which was “banana”) is now “mango”. The other items are unchanged.

3.3 Changing a Range of Items

You can replace several items at once using a slice:

fruits = ["apple", "banana", "cherry", "orange", "kiwi"]
fruits[1:3] = ["mango", "melon"]
print(fruits)

Expected output:

['apple', 'mango', 'melon', 'orange', 'kiwi']

Items at indexes 1 and 2 (“banana” and “cherry”) were replaced with “mango” and “melon”.

What if you replace a range with MORE items than the original range?

fruits = ["apple", "banana", "cherry"]
fruits[1:2] = ["mango", "melon", "grape"]
print(fruits)

Expected output:

['apple', 'mango', 'melon', 'grape', 'cherry']

Only index 1 (“banana”) was in the slice, but it was replaced by THREE items. The list grew longer!

What if you replace a range with FEWER items?

fruits = ["apple", "banana", "cherry", "orange"]
fruits[1:3] = ["mango"]
print(fruits)

Expected output:

['apple', 'mango', 'orange']

“banana” and “cherry” (2 items) were replaced by only “mango” (1 item). The list shrank.

3.4 Inserting an Item Without Replacing — insert()

insert(index, value) adds a new item at a specific position without removing anything:

fruits = ["apple", "banana", "cherry"]
fruits.insert(2, "watermelon")
print(fruits)

Expected output:

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

“watermelon” was inserted at position 2. “cherry” was pushed to position 3. Nothing was deleted.

Part 4 – Adding Items to a List

4.1 The Three Ways to Add Items

Method What it does
append(value) Adds one item to the end of the list
insert(index, value) Adds one item at a specific position
extend(iterable) Adds multiple items from another list (or any iterable) to the end

4.2 append() — Add to the End

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

Expected output:

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

append() is the most commonly used method for adding items. It always places the new item at the very end.

Second example — building a list step by step:

shopping = []
shopping.append("milk")
shopping.append("eggs")
shopping.append("bread")
print(shopping)

Expected output:

['milk', 'eggs', 'bread']

We started with an empty list [] and built it up one item at a time. This pattern is extremely common in real programs.

4.3 insert() — Add at a Specific Position

We already saw insert() in Part 3, but here it is as an add operation:

fruits = ["apple", "banana", "cherry"]
fruits.insert(1, "kiwi")
print(fruits)

Expected output:

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

“kiwi” was inserted at position 1. Everything from position 1 onwards was shifted right by one.

Insert at the beginning (position 0):

fruits = ["apple", "banana", "cherry"]
fruits.insert(0, "strawberry")
print(fruits)

Expected output:

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

4.4 extend() — Add Multiple Items from Another List

fruits = ["apple", "banana", "cherry"]
more_fruits = ["mango", "pineapple", "papaya"]
fruits.extend(more_fruits)
print(fruits)

Expected output:

['apple', 'banana', 'cherry', 'mango', 'pineapple', 'papaya']

Every item from more_fruits was added individually to the end of fruits.

extend() vs append() — the key difference:

fruits = ["apple", "banana"]

# append adds the whole list AS ONE item:
fruits.append(["mango", "kiwi"])
print(fruits)

Expected output:

['apple', 'banana', ['mango', 'kiwi']]

fruits = ["apple", "banana"]

# extend adds each item separately:
fruits.extend(["mango", "kiwi"])
print(fruits)

Expected output:

['apple', 'banana', 'mango', 'kiwi']

Common beginner mistake: Using append() when you meant extend(). The result is a nested list instead of a flat list.

extend() also works with other iterables like tuples:

fruits = ["apple", "banana", "cherry"]
fruits.extend(("kiwi", "orange"))
print(fruits)

Expected output:

['apple', 'banana', 'cherry', 'kiwi', 'orange']

Part 5 – Removing Items from a List

5.1 The Ways to Remove Items

Method / Keyword What it does
remove(value) Removes the first occurrence of a specific value
pop(index) Removes the item at a specific index (default: last item)
del list[index] Deletes item at a specific index, or deletes the whole list
clear() Empties the list completely (list still exists, but has no items)

5.2 remove() — Remove by Value

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

Expected output:

['apple', 'cherry']

“banana” was found and removed. The list shrank by one.

What if the value appears more than once?

remove() only deletes the first occurrence:

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

Expected output:

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

Only the first “banana” (at index 1) was removed. The second “banana” (originally at index 3) remains.

What if the value does not exist?

fruits = ["apple", "banana", "cherry"]
fruits.remove("mango")   # "mango" is not in the list

Expected output:

ValueError: list.remove(x): x not in list

Common beginner mistake: Calling remove() on a value that is not in the list. Always check first with in if you are unsure.

Safe version:

fruits = ["apple", "banana", "cherry"]
if "mango" in fruits:
    fruits.remove("mango")
else:
    print("mango was not found in the list")

Expected output:

mango was not found in the list

5.3 pop() — Remove by Index

pop() removes and returns the item at a given index. If no index is given, it removes the last item.

fruits = ["apple", "banana", "cherry"]
fruits.pop(1)
print(fruits)

Expected output:

['apple', 'cherry']

pop() without an index — removes the last item:

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

Expected output:

['apple', 'banana']

pop() returns the removed item — you can store it:

fruits = ["apple", "banana", "cherry"]
removed = fruits.pop(1)
print("Removed:", removed)
print("List now:", fruits)

Expected output:

Removed: banana
List now: ['apple', 'cherry']

This is very useful when you want to process the item you are removing.

5.4 del — Delete by Index or Slice

The del keyword deletes an item at a specific index:

fruits = ["apple", "banana", "cherry"]
del fruits[0]
print(fruits)

Expected output:

['banana', 'cherry']

Delete a slice:

fruits = ["apple", "banana", "cherry", "orange", "kiwi"]
del fruits[1:3]
print(fruits)

Expected output:

['apple', 'orange', 'kiwi']

Delete the entire list variable:

fruits = ["apple", "banana", "cherry"]
del fruits
# print(fruits)   # This would now cause a NameError — the variable no longer exists

After del fruits, the variable fruits is completely gone from memory. This is different from clear().

5.5 clear() — Empty the List

clear() removes all items from the list, but the list variable itself still exists:

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

Expected output:

[]

The list is now empty [], but fruits still exists as a variable. You can add new items to it later.

Part 6 – Guided Practice Exercises

Exercise 1 – Class Register

Objective: Create and display a list of student names.

Scenario: You are a teacher building a digital class register.

Steps:

  1. Create a list called students with five student names.
  2. Print the full list.
  3. Print just the first student.
  4. Print just the last student using negative indexing.
  5. Print the number of students using len().

Starter code:

students = ["Alice", "Bob", "Charlie", "Diana", "Eve"]
# Your code below:

Expected output:

['Alice', 'Bob', 'Charlie', 'Diana', 'Eve']
Alice
Eve
5

Self-check questions:

  • What index does “Charlie” have?
  • What would students[-2] return?
  • What would students[1:4] return?

Exercise 2 – Shopping Cart

Objective: Practice adding and removing items from a list.

Scenario: You are building a simple shopping cart.

Steps:

  1. Start with an empty list called cart.
  2. Use append() to add: “milk”, “eggs”, “bread”, “cheese”.
  3. Print the cart.
  4. The customer changed their mind — remove “eggs” using remove().
  5. Add “yoghurt” at position 1 using insert().
  6. Print the final cart.
  7. Print the total number of items.

Expected output:

['milk', 'eggs', 'bread', 'cheese']
['milk', 'yoghurt', 'bread', 'cheese']
4

Optional what-if challenge: What would happen if you used pop(0) instead of remove("eggs")?

Exercise 3 – Temperature Log

Objective: Practice slicing and modifying a list.

Scenario: A weather station recorded temperatures for a week (in °C).

temperatures = [22, 19, 25, 30, 28, 17, 21]
# Days:          Mon Tue Wed Thu  Fri  Sat Sun

Tasks:

  1. Print the temperature for Wednesday (index 2).
  2. Print temperatures for Tuesday to Friday (use slicing).
  3. The Saturday reading was wrong — it should be 20. Fix it.
  4. Print the updated list.
  5. Check whether the temperature 30 is in the list and print a message.

Expected output:

25
[19, 25, 30, 28]
[22, 19, 25, 30, 28, 20, 21]
30 degrees was recorded this week.

Exercise 4 – Combining Two Inventories

Objective: Practice using extend().

Scenario: Two warehouses need to merge their stock lists.

warehouse_a = ["screws", "bolts", "nails"]
warehouse_b = ["hammers", "drills", "saws"]
  1. Use extend() to merge warehouse_b into warehouse_a.
  2. Print the combined list.
  3. Use del to remove “bolts” by index.
  4. Print the final list.

Expected output:

['screws', 'bolts', 'nails', 'hammers', 'drills', 'saws']
['screws', 'nails', 'hammers', 'drills', 'saws']

Part 7 – Mini-Project: Student Grade Tracker

Project Overview

You will build a Student Grade Tracker — a small Python program that stores student names and their exam scores, allows grade updates, adds new students, and removes students who have withdrawn.

This project uses every skill from today’s lesson.

Stage 1 – Setup

Create two lists: one for student names, one for their scores. Each index position corresponds to the same student.

# Stage 1 – Create the lists
names  = ["Alice", "Bob", "Charlie", "Diana", "Eve"]
scores = [88, 74, 91, 65, 83]

print("Students:", names)
print("Scores:  ", scores)
print("Total students:", len(names))

Milestone output:

Students: ['Alice', 'Bob', 'Charlie', 'Diana', 'Eve']
Scores:   [88, 74, 91, 65, 83]
Total students: 5

Stage 2 – Access and Display

Print each student with their score using index access:

# Stage 2 – Access individual records
print("\n--- Grade Report ---")
print("First student:", names[0], "→ Score:", scores[0])
print("Last student: ", names[-1], "→ Score:", scores[-1])
print("Top 3 students:", names[:3], "→ Scores:", scores[:3])

Milestone output:

--- Grade Report ---
First student: Alice → Score: 88
Last student:  Eve → Score: 83
Top 3 students: ['Alice', 'Bob', 'Charlie'] → Scores: [88, 74, 91]

Stage 3 – Update a Score

Bob re-sat his exam and scored 85. Update his score:

# Stage 3 – Update Bob's score (Bob is at index 1)
scores[1] = 85
print("\nUpdated scores:", scores)
print("Bob's new score:", scores[1])

Milestone output:

Updated scores: [88, 85, 91, 65, 83]
Bob's new score: 85

Stage 4 – Add a New Student

A new student, Frank, joins with a score of 79:

# Stage 4 – Add a new student
names.append("Frank")
scores.append(79)

print("\nAfter adding Frank:")
print("Students:", names)
print("Scores:  ", scores)
print("Total:", len(names))

Milestone output:

After adding Frank:
Students: ['Alice', 'Bob', 'Charlie', 'Diana', 'Eve', 'Frank']
Scores:   [88, 85, 91, 65, 83, 79]
Total: 6

Stage 5 – Remove a Withdrawn Student

Diana has withdrawn from the course. Remove her:

# Stage 5 – Remove Diana
diana_index = names.index("Diana")   # Find her position
names.pop(diana_index)
scores.pop(diana_index)

print("\nAfter Diana withdrew:")
print("Students:", names)
print("Scores:  ", scores)
print("Total:", len(names))

Milestone output:

After Diana withdrew:
Students: ['Alice', 'Bob', 'Charlie', 'Eve', 'Frank']
Scores:   [88, 85, 91, 83, 79]
Total: 5

Stage 6 – Final Report

Display the complete final class list:

# Stage 6 – Final report
print("\n========== FINAL CLASS REPORT ==========")
for i in range(len(names)):
    print(f"  {names[i]:<10} Score: {scores[i]}")
print("=========================================")
print(f"Class size: {len(names)} students")

Milestone output:

========== FINAL CLASS REPORT ==========
  Alice      Score: 88
  Bob        Score: 85
  Charlie    Score: 91
  Eve        Score: 83
  Frank      Score: 79
=========================================
Class size: 5 students

Reflection Questions

  1. Why did we use names.index("Diana") before calling pop() instead of just using pop() directly?
  2. What would happen if two students had the same name and you called names.index() on that name?
  3. How would you modify this project to also track each student’s letter grade (A, B, C, etc.)?
  4. Could you use a single list of lists (nested lists) instead of two parallel lists? What would that look like?

Optional Extensions

  • Calculate and print the average score
  • Find and print the highest and lowest score using max() and min()
  • Sort students alphabetically using .sort()
  • Add a function that searches for a student by name and returns their score

Part 8 – Common Beginner Mistakes (Summary)

Mistake 1 – IndexError: Index Out of Range

# WRONG
fruits = ["apple", "banana", "cherry"]
print(fruits[3])   # Only indexes 0, 1, 2 exist!

IndexError: list index out of range

Fix: Remember that a list of n items has indexes 0 to n-1. Use len(fruits) - 1 for the last valid index.

Mistake 2 – Confusing append() and extend()

# WRONG – adds nested list
fruits = ["apple", "banana"]
fruits.append(["cherry", "mango"])
print(fruits)   # ['apple', 'banana', ['cherry', 'mango']]

Fix: Use extend() when you want to add multiple items individually:

fruits = ["apple", "banana"]
fruits.extend(["cherry", "mango"])
print(fruits)   # ['apple', 'banana', 'cherry', 'mango']

Mistake 3 – remove() on a Non-Existent Value

# WRONG
fruits = ["apple", "banana"]
fruits.remove("grape")   # ValueError!

Fix: Check first with in:

if "grape" in fruits:
    fruits.remove("grape")

Mistake 4 – Forgetting That Slicing Does NOT Include the End Index

fruits = ["apple", "banana", "cherry", "orange"]
print(fruits[1:3])   # Returns items at index 1 AND 2 — NOT 3

['banana', 'cherry']

The slice [1:3] means “from index 1 up to but NOT including index 3”.

Mistake 5 – del vs clear() vs Setting to []

fruits = ["apple", "banana"]

# del removes the variable entirely
del fruits
# print(fruits)   # NameError — 'fruits' does not exist!

# clear() empties the list, but the variable still exists
fruits = ["apple", "banana"]
fruits.clear()
print(fruits)     # []  — variable exists, just empty

# Assigning [] replaces the list with a new empty one
fruits = ["apple", "banana"]
fruits = []
print(fruits)     # []

Mistake 6 – Modifying a List While Looping Over It

This is an advanced mistake to be aware of. Avoid removing items from a list inside a for loop that is iterating over the same list — it causes unexpected behaviour. Use a copy or a different approach.

Reflection Questions

  1. What is the difference between a list and a simple variable?
  2. Why does Python start list indexes at 0 instead of 1?
  3. When would you use pop() instead of remove()?
  4. What is the difference between append() and extend()?
  5. What happens to the list after you call clear() — does the variable disappear?
  6. How would you get the last three items of a list without knowing its exact length?
  7. What does del my_list do that is different from my_list.clear()?
  8. If a list has 7 items, what is the index of the last item?

Completion Checklist

Before moving on, confirm you can:

  • Create a list using square brackets []
  • Create an empty list and build it up using append()
  • Access any item by its positive index
  • Access items using negative indexes
  • Slice a list to get a range of items
  • Check whether a value is in a list using in
  • Change a single item by assigning to its index
  • Change multiple items using slice assignment
  • Add an item to the end with append()
  • Add an item at a specific position with insert()
  • Merge another list using extend()
  • Remove an item by value with remove()
  • Remove an item by index with pop()
  • Delete an item with del
  • Empty a list with clear()
  • Explain the difference between append() and extend()
  • Explain the difference between del and clear()
  • Complete the Student Grade Tracker mini-project

Lesson Summary

In this lesson you learned everything about Python lists — one of the most fundamental and powerful tools in the entire language.

What a list is: An ordered, changeable collection of items, written with square brackets and commas. Lists allow duplicate values and can hold any data type — including other lists.

How to access items: Use a zero-based index in square brackets. Negative indexes count from the end. Slicing ([start:end]) extracts a section of the list. The in keyword checks for membership.

How to change items: Assign a new value to an index (list[0] = "new"). Assign to a slice to replace multiple items at once. Use insert(index, value) to add without replacing.

How to add items: Use append(value) for the end, insert(index, value) for a specific position, and extend(iterable) to add all items from another list.

How to remove items: Use remove(value) to delete by value (first occurrence), pop(index) to delete by index (and optionally capture the removed value), del list[index] to delete by index or slice, and clear() to empty the list entirely.

Why this matters in the real world: Lists power virtually every Python application — from storing datasets in data science, to managing game objects, to tracking inventory in business systems, to building web application features. Mastering lists is one of the most important milestones in learning Python.

End of Lesson 07 – Python Lists