132.1 Lists

Learn how to use lists to store and manipulate multiple values in a single variable.

What is a list?

A list is a data structure that stores a sequence of values. In Python, a list is implemented as a dynamic array, which means it can change size during execution and store items of any data type, even mixed types within the same list.

In most programming languages, an array is a fixed-size structure that stores elements of only one type (e.g. integers or floats). Python lists are more flexible than traditional arrays because:

• They are mutable (can be changed after creation)

• They can grow and shrink dynamically

• They can store different types of values together (e.g. strings, numbers, Booleans)

Pseudocode

SET example_list TO LIST ["Alice", 10, TRUE]

Python

# A string, an integer, and a Boolean in one list
example_list = ["Alice", 10, True]

This makes Python lists powerful and convenient for general-purpose programming, though they may be less efficient than typed arrays for large-scale numerical operations.

Creating a list

In Python, you create a list using square brackets. In pseudocode, we use a LIST declaration with an initial size or contents.

Pseudocode

SET names TO LIST ["Lina", "Ari", "Noah"]

Python

names = ["Lina", "Ari", "Noah"]

Accessing and modifying list items

Each item in a list can be accessed using its index. Indices usually start at 0 in most languages, including Python.

Pseudocode

SET names TO LIST ["Lina", "Ari", "Noah"]
OUTPUT names[0]         // Lina
SET names[1] TO "Aria"  // LIST ["Lina", "Aria", "Noah"]

Python

names = ["Lina", "Ari", "Noah"]
print(names[0])       # Lina
names[1] = "Aria"     # names = ["Lina", "Aria", "Noah"]

Adding and removing items

Lists are dynamic, which means you can append, insert, or remove elements at runtime.

Pseudocode

SET names TO LIST ["Lina", "Ari", "Noah"]
APPEND "Zane" TO names               // LIST ["Lina", "Ari", "Noah", "Zane"]
INSERT "Kai" AT POSITION 1 IN names. // LIST ["Lina", "Kai", "Ari", "Noah", "Zane"]
REMOVE "Lina" FROM names             // LIST ["Kai", "Ari", "Noah", "Zane"]

Python

names.append("Zane")        # Add to the end
names.insert(1, "Kai")      # Insert at index 1
names.remove("Lina")        # Remove by value

Looping through a list

Lists are often used with loops to process each element.

Pseudocode

FOR name IN names
    OUTPUT name
ENDFOR

Python

for name in names:
    print(name)

Useful list functions and methods

Task	Python	Pseudocode
Find length	len(names)	LENGTH(names)
Check membership	"Kai" in names	"Kai" IN names
Sort items	names.sort()	SORT names
Reverse items	names.reverse()	REVERSE names

Key concepts

• A list stores multiple values in one variable and can be modified during runtime.

• List items are accessed using an index.

• Lists support operations like append, insert, remove, and iteration.

• Lists are essential for storing dynamic collections such as user inputs or game scores.