Working with lists¶

In this tutorial, you will learn how to create, modify, and iterate over lists in Python.

Time commitment: 15–20 minutes

Prerequisites:

• Python 3.12 or later installed on your machine
• Basic familiarity with Python syntax (variables, strings, numbers)

Learning objectives¶

By the end of this tutorial, you will be able to:

• Create lists and access items by index
• Add, remove, and modify items in a list
• Iterate over lists using for loops
• Use slicing to extract parts of a list

What is a list?¶

A list is an ordered, mutable collection of items. Lists are one of the most commonly used data structures in Python. You can store any type of item in a list — numbers, strings, or even other lists.

Lists are created using square brackets []:

In [ ]:

fruits = ["apple", "banana", "cherry"]
print(fruits)

fruits = ["apple", "banana", "cherry"] print(fruits)

Accessing items by index¶

Each item in a list has a position called an index. Python uses zero-based indexing, which means the first item is at index 0:

In [ ]:

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

print(fruits[0])  # First item
print(fruits[1])  # Second item
print(fruits[2])  # Third item

fruits = ["apple", "banana", "cherry"] print(fruits[0]) # First item print(fruits[1]) # Second item print(fruits[2]) # Third item

You can also use negative indices to count from the end of the list. The index -1 refers to the last item:

In [ ]:

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

print(fruits[-1])  # Last item
print(fruits[-2])  # Second to last

fruits = ["apple", "banana", "cherry"] print(fruits[-1]) # Last item print(fruits[-2]) # Second to last

Finding the length of a list¶

Use the built-in len() function to find out how many items are in a list:

In [ ]:

fruits = ["apple", "banana", "cherry"]
print(len(fruits))

fruits = ["apple", "banana", "cherry"] print(len(fruits))

Adding items¶

Lists are mutable, which means you can change them after they are created. Use append() to add an item to the end of a list:

In [ ]:

fruits = ["apple", "banana"]
fruits.append("cherry")
print(fruits)

fruits = ["apple", "banana"] fruits.append("cherry") print(fruits)

Use insert() to add an item at a specific position:

In [ ]:

fruits = ["apple", "cherry"]
fruits.insert(1, "banana")  # Insert at index 1
print(fruits)

fruits = ["apple", "cherry"] fruits.insert(1, "banana") # Insert at index 1 print(fruits)

Removing items¶

Use remove() to remove a specific item by its value:

In [ ]:

fruits = ["apple", "banana", "cherry"]
fruits.remove("banana")
print(fruits)

fruits = ["apple", "banana", "cherry"] fruits.remove("banana") print(fruits)

Use pop() to remove an item by its index (and get it back):

In [ ]:

fruits = ["apple", "banana", "cherry"]
removed = fruits.pop(1)  # Remove item at index 1
print(f"Removed: {removed}")
print(f"Remaining: {fruits}")

fruits = ["apple", "banana", "cherry"] removed = fruits.pop(1) # Remove item at index 1 print(f"Removed: {removed}") print(f"Remaining: {fruits}")

Iterating over a list¶

Use a for loop to go through each item in a list:

In [ ]:

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

for fruit in fruits:
    print(f"I like {fruit}!")

fruits = ["apple", "banana", "cherry"] for fruit in fruits: print(f"I like {fruit}!")

If you need the index as well as the value, use enumerate():

In [ ]:

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

for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

fruits = ["apple", "banana", "cherry"] for index, fruit in enumerate(fruits): print(f"{index}: {fruit}")

Slicing¶

Slicing lets you extract a portion of a list. The syntax is list[start:stop], where start is included and stop is excluded:

In [ ]:

numbers = [0, 1, 2, 3, 4, 5]

print(numbers[1:4])   # Items at index 1, 2, 3
print(numbers[:3])    # First three items
print(numbers[3:])    # Everything from index 3 onwards
print(numbers[-2:])   # Last two items

numbers = [0, 1, 2, 3, 4, 5] print(numbers[1:4]) # Items at index 1, 2, 3 print(numbers[:3]) # First three items print(numbers[3:]) # Everything from index 3 onwards print(numbers[-2:]) # Last two items

Checking membership¶

Use the in keyword to check whether an item exists in a list:

In [ ]:

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

print("banana" in fruits)
print("grape" in fruits)

fruits = ["apple", "banana", "cherry"] print("banana" in fruits) print("grape" in fruits)

Exercise: build a to-do list¶

Now it is your turn! Create a list of three tasks you need to do today. Then:

1. Add a fourth task
2. Remove the second task (you have already done it)
3. Print the remaining tasks with their positions

In [ ]:

# Write your code here

# Write your code here

Solution¶

Here is one way to complete the exercise:

In [ ]:

tasks = ["Buy groceries", "Reply to emails", "Go for a walk"]

# Add a fourth task
tasks.append("Read a chapter")

# Remove the second task
tasks.pop(1)

# Print remaining tasks with positions
for index, task in enumerate(tasks, start=1):
    print(f"{index}. {task}")

tasks = ["Buy groceries", "Reply to emails", "Go for a walk"] # Add a fourth task tasks.append("Read a chapter") # Remove the second task tasks.pop(1) # Print remaining tasks with positions for index, task in enumerate(tasks, start=1): print(f"{index}. {task}")

Summary¶

In this tutorial, you learned how to:

• Create lists using square brackets []
• Access items using positive and negative indices
• Add items with append() and insert()
• Remove items with remove() and pop()
• Iterate over lists with for loops and enumerate()
• Extract portions of a list using slicing
• Check whether an item exists using in

What is next¶

In upcoming tutorials, you will explore:

• Tuples — immutable sequences for data that should not change
• Dictionaries — key-value pairs for fast lookups
• Sets — collections of unique items
• Comprehensions — concise ways to build data structures