List Basics

Store and access ordered collections of items

List Basics — Storing Collections of Data

What Is a List?

A list is an ordered collection of items. Instead of creating 10 separate variables (fruit1, fruit2, fruit3...), you put them all in one list. Lists are the most versatile and commonly used data structure in Python.

� **Analogy:** A list is like a numbered shopping list. Each item has a position (index), and you can look up items by their position.

Syntax

python

fruits = ["apple", "banana", "cherry", "date"]
#          0         1         2         3
#         -4        -3        -2        -1
print(fruits[0])    # "apple"  — index 0 is the FIRST item
print(fruits[-1])   # "date"   — index -1 is the LAST item
print(len(fruits))  # 4 — total number of items

Part	What it means
`fruits = [...]`	Creates a list (square brackets)
`"apple"`	An item in the list (separated by commas)
`fruits[0]`	Accesses the item at index 0 (first position)
`fruits[-1]`	Access using negative index (counts from end)
`len(fruits)`	Returns the number of items

How It Works — Indexing

Python lists are zero-indexed — the first item is at position 0, not 1.

python

colors = ["red", "green", "blue", "yellow"]

print(colors[0])    # red     — 1st item
print(colors[1])    # green   — 2nd item  
print(colors[2])    # blue    — 3rd item
print(colors[3])    # yellow  — 4th item
print(colors[-1])   # yellow  — last item (shorthand!)
print(colors[-2])   # blue    — second to last

� **Key insight:** Index 0 = first item. Index 1 = second item. It's confusing at first, but every programmer deals with zero-based indexing. You'll get used to it!

Lists Can Hold Any Type

python

mixed = [42, "hello", 3.14, True, None]  # Any type works
nested = [[1, 2], [3, 4]]                # Lists inside lists!

Why Use Lists?

Lists are everywhere in programming:

**Todo apps** — list of tasks

**Shopping carts** — list of items the user picked

**Search results** — list of matching products

**Spreadsheet rows** — list of cell values

**Game inventories** — list of items the player holds

Common Mistakes

❌ Wrong	Why	✅ Right
`colors = "red", "green", "blue"`	That creates a tuple (parentheses), not a list	`colors = ["red", "green", "blue"]`
`colors[1]` expecting "red"	Index 0 is the first item!	`colors[0]` for "red"
`fruits[len(fruits)]`	Index out of range — indexes go 0 to len-1	`fruits[len(fruits) - 1]` or `fruits[-1]`
Forgetting commas between items	Syntax error	Separate items with commas

Your Turn!

Create a list called animals with three animals (strings). Then:

Print the first animal

Print the last animal (using a negative index)

Print how many animals are in the list

💡Need a hint? (3 available)

#1Index 0 is the first item, not index 1

#2Use [-1] to get the last item

#3Use len(list) to get the number of items

🔑Show solution (try it yourself first!)

animals = ["cat", "dog", "bird"]
print(animals[0])
print(animals[-1])
print(len(animals))

✏️ Code Editor

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📤 Output

Write your solution and click "Run Code" to test it!

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