409 Conflict in Rest API - Mini Project: Build & Apply

Handling 409 Conflict in REST API

📖 Scenario: You are building a simple REST API for managing a list of usernames. The API should prevent adding duplicate usernames.

🎯 Goal: Create a REST API endpoint that adds a username to a list. If the username already exists, the API should respond with a 409 Conflict status code and a clear message.

📋 What You'll Learn

Create a list called usernames with initial usernames

Create a variable called new_username with a username to add

Write code to check if new_username is already in usernames

If it exists, respond with status code 409 and message 'Username already exists'

If it does not exist, add new_username to usernames and respond with status code 201 and message 'Username added'

💡 Why This Matters

🌍 Real World

APIs often need to prevent duplicate entries like usernames or emails. Returning a 409 Conflict status helps clients understand the problem clearly.

💼 Career

Backend developers and API designers must handle conflicts gracefully to build reliable and user-friendly services.

1

Create initial usernames list

Create a list called usernames with these exact values: 'alice', 'bob', 'charlie'

Rest API

# Create the list usernames with 'alice', 'bob', 'charlie'
# Your code here

Need a hint?

Use square brackets to create a list and separate items with commas.

2

Set the new username to add

Create a variable called new_username and set it to the string 'bob'

Rest API

usernames = ['alice', 'bob', 'charlie']
# Create new_username and set it to 'bob'
# Your code here

Need a hint?

Assign the string 'bob' to the variable new_username.

3

Check for duplicate and prepare response

Write an if statement to check if new_username is in usernames. If yes, create a variable status_code with value 409 and a variable message with value 'Username already exists'. Otherwise, add new_username to usernames, set status_code to 201, and message to 'Username added'.

Rest API

usernames = ['alice', 'bob', 'charlie']
new_username = 'bob'
# Check if new_username is in usernames and set status_code and message accordingly
# Your code here

Need a hint?

Use if new_username in usernames: to check duplicates and append() to add new usernames.

4

Print the API response

Print the status_code and message variables in this exact format: Status: <status_code>, Message: <message>

Rest API

usernames = ['alice', 'bob', 'charlie']
new_username = 'bob'
if new_username in usernames:
    status_code = 409
    message = 'Username already exists'
else:
    usernames.append(new_username)
    status_code = 201
    message = 'Username added'
# Print the status_code and message in the format: Status: , Message: 
# Your code here

Need a hint?

Use an f-string to format the print output exactly as shown.