Key Terms

• Lists – Ordered collections of items stored in square brackets ([ ]).

• Indexing – Accessing elements in a list using their position (fruits[0] gets the first item).

• Appending – Adding new elements to a list using .append() (fruits.append("grape")).

• len(myList) - 

• List slicing – Extracting a portion of a list using indices (fruits[1:3]).

• Mutable data structures – Lists can be changed after creation by adding, removing, or modifying elements.

Creating & Using Lists

1. Creating a List

In Python, a list is a way to store multiple values in a single variable. You can create a list by placing items inside square brackets [], separated by commas.

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

print(fruits)

2. Accessing List Elements

Each item in a list has a position (called an index), starting from 0. You can access items using these indices, including negative numbers to count from the end.

print(fruits[0])  # First element

print(fruits[-1])  # Last element

3. Appending List Elements

You can start with an empty list and add elements to it using the .append() method. This is useful when you're building a list dynamically.

students = []

students.append("Liam")

students.append("Sofia")

students.append("Carlos")

print(students) #prints all elements in the list

4. Looping through a list 

Using a for loop, you can go through each item in a list and do something with it, like print a message.

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

for fruit in fruits:

    print("I like", fruit) #outputs the elements one at a time

5. Looping through list using len()

Sometimes you want to loop through a list using index numbers. You can use range(len(list)) to do that and access each item by its index.

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

for i in range(len(fruits)):

    print("Fruit", i, "is", fruits[i]) #outputs using index-value

🛑 Common Mistakes with Lists

Forgetting that lists start at index 0: In a list with 3 items, list[3] will cause an IndexError. You should use list[0], list[1], and list[2].

Overwriting a list accidentally when using .append()
Example:
Incorrect: fruits = fruits.append("orange") (this changes fruits to None)
Correct: fruits.append("orange") (this adds "orange" to the list properly)

Mixing up brackets: Always use square brackets [ ] for lists. Round brackets ( ) are for functions or tuples.

Using = instead of .append() to add items
Example:
Incorrect: fruits = "apple" (this replaces the whole list)
Correct: fruits.append("apple") (this adds a new item without losing the list)

Trying to print multiple items without a loop or index: print(list) shows the whole list at once, but if you want to print each item separately, you need a for loop.

Forgetting quotation marks around strings
Incorrect: fruits = [apple, banana]
Correct: fruits = ["apple", "banana"]

Forgetting commas between list items
Incorrect: fruits = ["apple" "banana" "orange"]
Correct: fruits = ["apple", "banana", "orange"]