Lists — Basics

Storing many things together

So far, every variable we have created holds a single piece of data: one string, one integer, one boolean.

But what if you are writing a to-do list app? You can't create task1, task2, task3, ... up to task100. That would be a nightmare.

You need a single container that can hold multiple items. In Python, the most common container is the List.

Creating a List

Lists are created using square brackets [], with commas separating the items.

python
# A list of strings
fruits = ["apple", "banana", "cherry"]

# A list of numbers
scores = [95, 82, 100, 75]

# A mixed list (Python doesn't mind!)
mixed_box = ["hello", 42, True, 3.14]

# An empty list
empty_list = []

Accessing items in a list

Does string indexing and slicing look familiar? Lists use the exact same system!

Lists are zero-indexed.

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

# Get the first item
print(fruits[0])  # Output: apple

# Get the third item
print(fruits[2])  # Output: cherry

# Get the last item using negative indexing
print(fruits[-1]) # Output: date

You can even slice out chunks of a list just like you did with strings:

python
# Get a new list with items from index 1 up to (but not including) index 3
print(fruits[1:3]) # Output: ['banana', 'cherry']

Finding the length

Just like strings, you can use the built-in len() function to find out how many items are inside a list.

python
colors = ["red", "green", "blue"]
amount = len(colors)
print(f"There are {amount} colors.") # Output: There are 3 colors.

Lists and for loops are best friends

Lists are meant to be iterated over. for loops make this incredibly elegant.

python
guests = ["Alice", "Bob", "Charlie"]

for guest in guests:
    print(f"Welcome to the party, {guest}!")

What this lesson should give you

After this lesson, you should understand how to:

• create a list using square brackets []
• access individual list items using zero-based indexing like my_list[0]
• grab the last item using my_list[-1]
• find the number of items in a list using the len() function
• elegantly iterate through every item in a list using a for loop