Learn Python in 30 Days — Day 10: Lists

Welcome to Day 10 of the Learn Python in 30 Days series!

All example files for this series are available on my GitHub: Learn-Python-in-30-Days

Last time we explored while loops and saw how to repeat tasks until a condition changes.
Today, you’ll learn about one of Python’s most useful tools, lists and use them to build your very first Shopping List Manager.

Step 1 – What Is a List?

A list is like a digital container that holds multiple pieces of data — numbers, words, or even other lists.

groceries = ["milk", "bread", "eggs"]
print(groceries)

Output:

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

You can store anything inside a list it’s one of Python’s most flexible data structures.

Try it yourself, hopefully you'll see something like that shown below: -

You can also download this example from my GitHub here and run it yourself.

Step 2 – Indexing (Accessing Items)

Each item in a list has a position (index).
Python starts counting at 0.

groceries = ["milk", "bread", "eggs"]
print(groceries[0])   # milk
print(groceries[2])   # eggs

Try changing a value:

groceries[1] = "butter"
print(groceries)

Try it yourself, hopefully you'll see something like that shown below: -
You can also download this example from my GitHub here and run it yourself.

Step 3 – Slicing (Getting Parts of a List)

Slicing allows you to extract sections of a list — like cutting a loaf of bread into smaller pieces.

The basic syntax is:

list_name[start:end]

• start → the index to begin at (included)

• end → the index to stop before (excluded)

Python doesn’t count the final position in the slice — this is called end-exclusive indexing.

Let’s see it in action:

numbers = [10, 20, 30, 40, 50]

print(numbers[1:4])   # [20, 30, 40]
print(numbers[:3])    # first three items
print(numbers[-2:])   # last two items

Here’s what happens visually:

Index	Value
0	10
1	20
2	30
3	40
4	50

• numbers[1:4] → starts at index 1 (20) and stops before 4 → [20, 30, 40]

• numbers[:3] → starts from the beginning and goes up to (but not including) index 3 → [10, 20, 30]

• numbers[-2:] → starts from the second last item and goes to the end → [40, 50]

You can even use a step value to skip through items:

numbers = [10, 20, 30, 40, 50, 60, 70]
print(numbers[::2])   # every second item → [10, 30, 50, 70]
print(numbers[1::2])  # every second item starting from index 1 → [20, 40, 60]

This is super useful when processing large data lists, generating sequences, or splitting text.

Tip: Negative slicing is powerful too.

print(numbers[::-1])  # reverses the list!

Try it yourself, hopefully you'll see something like that shown below: -

You can also download this example from my GitHub here and run it yourself.

Step 4 – Adding & Removing Items

Lists are dynamic, meaning you can grow or shrink them freely — no need to declare sizes like in other programming languages.

Let’s begin:

groceries = ["milk", "bread"]
groceries.append("eggs")       # Add item to the end
print(groceries)

Output:

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

Adding Items

There are several ways to add data:

# Add one item
groceries.append("butter")

# Add multiple items
groceries.extend(["cheese", "apples"])

# Insert at a specific position
groceries.insert(1, "coffee")  # index 1, before 'bread'

Result:

['milk', 'coffee', 'bread', 'eggs', 'butter', 'cheese', 'apples']

Removing Items

You can remove items by name, index, or method:

groceries.remove("bread")      # remove a specific item
print(groceries)

del groceries[0]               # delete by index (0 = first)
print(groceries)

popped = groceries.pop()       # removes and returns the last item
print("Removed:", popped)
print(groceries)

Clearing the List

If you ever want to start fresh:

groceries.clear()
print(groceries)  # []

Quick Recap

Action	Method	Example
Add one item	.append(x)	groceries.append("milk")
Add many	.extend([...])	groceries.extend(["eggs", "bread"])
Insert anywhere	.insert(index, x)	groceries.insert(0, "coffee")
Remove by value	.remove(x)	groceries.remove("bread")
Remove by index	del	del groceries[2]
Remove last & return	.pop()	groceries.pop()
Clear all	.clear()	groceries.clear()

Try it yourself, hopefully you'll see something like that shown below: -

You can also download this example from my GitHub here and run it yourself.

Step 5 – Looping Through a List

Combine what you learned from for loops:

groceries = ["milk", "bread", "eggs"]
for item in groceries:
    print(f"- {item}")

Output:

- milk
- bread
- eggs

Try it yourself, hopefully you'll see something like that shown below: -

You can also download this example from my GitHub here and run it yourself.

Mini-Project – Shopping List Manager

Now let’s use lists to build a real mini-program!

# Shopping List Manager

shopping_list = []

while True:
    print("\nYour list:", shopping_list)
    print("Options: add, remove, quit")
    choice = input("What would you like to do? ").lower()

    if choice == "add":
        item = input("Enter item to add: ")
        shopping_list.append(item)
        print(f"{item} added!")

    elif choice == "remove":
        item = input("Enter item to remove: ")
        if item in shopping_list:
            shopping_list.remove(item)
            print(f"{item} removed.")
        else:
            print("Item not found.")

    elif choice == "quit":
        print("Final list:", shopping_list)
        break

    else:
        print("Invalid option.")

How it works

• Starts with an empty list

• Lets you add or remove items in a loop

• Ends when the user types “quit”

You’ve just created an interactive, data-driven program! Hopefully you'll see something like that shown below: -

You can also download this example from my GitHub here and run it yourself.

Next up — Day 11 – Tuples & Sets

All example files for this series are available on my GitHub: Learn-Python-in-30-Days

You can see the full series here Learn Python in 30 Days series!

Hope you have enjoyed this post, thanks Matty