Idempotency keys for safe retries in Rest API - Mini Project: Build & Apply

Idempotency Keys for Safe Retries in REST API

📖 Scenario: You are building a simple REST API that processes payment requests. Sometimes, clients may retry the same request if they don't get a response quickly. To avoid charging twice, your API needs to handle these retries safely.

🎯 Goal: Build a REST API endpoint that uses idempotency_key to ensure repeated requests with the same key do not cause duplicate processing.

📋 What You'll Learn

Create a dictionary to store processed idempotency keys and their results

Add a variable to hold the current request's idempotency key

Use logic to check if the idempotency key was seen before and return the stored result if yes

Print the final response for the request

💡 Why This Matters

🌍 Real World

Idempotency keys are used in payment systems and APIs to prevent duplicate charges or actions when clients retry requests due to network issues.

💼 Career

Understanding idempotency keys is important for backend developers and API designers to build reliable and safe services.

1

Create storage for processed requests

Create a dictionary called processed_requests that will store idempotency keys as keys and their results as values.

Rest API

# Create a dictionary called processed_requests to store idempotency keys and results
# Your code here

Need a hint?

Use curly braces {} to create an empty dictionary.

2

Add current request's idempotency key

Create a variable called idempotency_key and set it to the string 'abc123' to represent the current request's unique key.

Rest API

processed_requests = {}
# Create a variable called idempotency_key and set it to 'abc123'
# Your code here

Need a hint?

Use quotes to create a string value.

3

Check and store result using idempotency key

Write an if statement to check if idempotency_key is in processed_requests. If yes, set result to the stored value. Otherwise, set result to 'Payment processed' and store it in processed_requests with the key idempotency_key.

Rest API

processed_requests = {}
idempotency_key = 'abc123'
# Check if idempotency_key is in processed_requests
# If yes, set result to stored value
# Else, set result to 'Payment processed' and store it
# Your code here

Need a hint?

Use if key in dict to check presence, and dictionary assignment to store values.

4

Print the final result

Write a print statement to display the value of result.

Rest API

processed_requests = {}
idempotency_key = 'abc123'

if idempotency_key in processed_requests:
    result = processed_requests[idempotency_key]
else:
    result = 'Payment processed'
    processed_requests[idempotency_key] = result

# Print the result
# Your code here

Need a hint?

Use print(result) to show the output.