Rest Api
Master building robust API clients, handling authentication, retries, pagination, webhooks, and async operations for production-grade integrations
Learn Python, JavaScript, Java and more with free interactive lessons, real projects and AI-powered help. Beginner-friendly.
Part of the free Python course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.
What You'll Learn
What Is a REST API Client?
A REST API client is code that sends HTTP requests to external services and receives structured responses. Every modern application integrates with external APIs for payments, data, AI, authentication, and more.
Core Capabilities
Common Use Cases
HTTP Methods Overview
GET - Retrieve Data
Fetch resources without side effects. Safe and idempotent.
POST - Create Resources
PUT/PATCH - Update
Modify existing resources. PUT replaces, PATCH updates partially.
DELETE - Remove
The Requests Library
requests is Python's most popular HTTP library. Simple, elegant, and widely used.
Installation
Key Features
Building Reusable API Clients
Instead of scattering API calls throughout your codebase, create a dedicated client class that centralizes:
This pattern is used by every major Python SDK (Stripe, OpenAI, AWS, etc.).
Error Handling & Retries
Types of Failures
Retry Strategy
Authentication Strategies
Bearer Tokens
API Keys
OAuth 2.0
Async API Clients with aiohttp
For high-performance applications that need to make many concurrent API calls, async clients are essential.
Benefits of Async
Use Cases
Pagination Patterns
Offset-Based Pagination
Simple but can be inefficient for large datasets.
Cursor-Based Pagination
Token-Based Pagination
Webhooks & Security
What Are Webhooks?
Webhooks are reverse APIs - the external service calls your endpoint when events occur.
HMAC Signature Verification
Always verify webhook signatures to prevent fake requests:
Rate Limiting & Circuit Breakers
Rate Limiting
Prevent exceeding API quotas by implementing client-side rate limiting:
Circuit Breaker Pattern
Prevent cascading failures when external services are down:
Response Validation with Pydantic
External APIs can return inconsistent data. Use Pydantic to validate and transform responses:
This is critical for production systems that depend on external data.
File Operations
Uploading Files
Use multipart/form-data for file uploads. Key considerations:
Downloading Files
NEVER load entire files into memory. Use streaming:
Professional SDK Structure
Well-designed API clients follow this structure:
This separation makes the codebase maintainable, testable, and extensible.
Best Practices Summary
✓ Always Do
✗ Never Do
Key Takeaways
Practice quiz
Which HTTP method fetches data without changing anything on the server?
- GET
- POST
- DELETE
- PUT
Answer: GET. GET retrieves resources and is safe and idempotent — it has no side effects.
Which method is used to create a new resource on the server?
- GET
- POST
- PATCH
- DELETE
Answer: POST. POST submits data to create new resources (like placing an order).
What is the difference between PUT and PATCH?
- PUT replaces the resource; PATCH updates it partially
- PUT deletes; PATCH creates
- They are identical
- PATCH replaces; PUT updates partially
Answer: PUT replaces the resource; PATCH updates it partially. PUT replaces the whole resource; PATCH applies a partial update.
In requests, which call makes a GET with a timeout?
- requests.fetch(url)
- requests.get(url, timeout=5)
- requests.read(url)
- requests.GET(url)
Answer: requests.get(url, timeout=5). requests.get(url, timeout=5) issues a GET and fails cleanly if the server is too slow.
How do you send a JSON body in a POST with requests?
- requests.post(url, data=data)
- requests.post(url, json=data)
- requests.post(url, body=data)
- requests.post(url, params=data)
Answer: requests.post(url, json=data). json=data serializes the dict and sets Content-Type to application/json automatically.
What does response.raise_for_status() do?
- Prints the status code
- Raises an exception on 4xx or 5xx responses
- Returns True for any response
- Retries the request
Answer: Raises an exception on 4xx or 5xx responses. It turns a failed (4xx/5xx) response into a catchable HTTPError instead of continuing silently.
A 429 status code means what?
- Not found
- Server error
- Rate limited — slow down and retry
- Success
Answer: Rate limited — slow down and retry. 429 Too Many Requests signals rate limiting; respect the Retry-After header and back off.
Which status code family indicates a SERVER error worth retrying?
- 2xx
- 3xx
- 4xx
- 5xx
Answer: 5xx. 5xx codes are server-side failures; 4xx are client errors that should not simply be retried.
What is the recommended retry strategy for transient failures?
- Retry instantly forever
- Exponential backoff with a max attempt limit
- Never retry
- Retry only POST requests
Answer: Exponential backoff with a max attempt limit. Use exponential backoff (1s, 2s, 4s...) with jitter and a cap, retrying safe operations.
Why use a requests.Session() object?
- To make requests slower
- For connection pooling and shared headers/cookies
- To avoid timeouts
- It is required for every request
Answer: For connection pooling and shared headers/cookies. A Session reuses the underlying connection pool and persists headers and cookies across calls.