Gen-AI Developer Classroom notes 25/Oct/2025

HTTP

• This is a standard protocol for communication
• HTTP:
  • Request
    • Verb (Method):
      • GET
      • POST
      • PUT
      • DELETE
      • HEAD
    • URL
    • HEADERS:
    • Body
  • Response
    • Status Code
    • Body
    • Headers
• HTTP Protocol can work with any form of data

REST APIs (Representational state transfer)

• REST APIs are not protocols but an style of implementing Services
• Concepts:
  • Resources
  • Methods
• REST API Principles

| Principle | Description | Example / Notes |
| ———————————– | ——————————————————————————————————————————————– | ——————————————————————————————- |
| 1. Client-Server Separation | The client (frontend/UI) and server (backend/data) are independent. The client only needs to know the API endpoints, not how data is stored. | A mobile app calls /api/doctors — it doesn’t care if data comes from MySQL or MongoDB. |
| 2. Statelessness | Each API request must contain all necessary information; the server doesn’t store client session state between requests. | Every request includes authentication token (like JWT) and required data. |
| 3. Uniform Interface | REST APIs follow a consistent, predictable structure for endpoints, HTTP methods, and responses. | Use nouns (/patients/1), not verbs (/getPatient); use standard HTTP methods. |
| 4. Resource-Based | Everything is treated as a resource (patients, doctors, appointments), and each has a unique URI. | /api/appointments/101 uniquely identifies an appointment. |
| 5. Use of HTTP Methods Properly | Use standard HTTP verbs for CRUD: GET, POST, PUT, DELETE, PATCH. | GET /patients → read, POST /patients → create. |
| 6. Representations | A resource can be represented in multiple formats like JSON, XML, or HTML. | Typically, REST APIs use JSON for simplicity. |
| 7. Layered System | The API can have multiple layers — authentication, caching, load balancer — without the client knowing. | Client only sees /api/appointments, not the backend structure. |
| 8. Cacheability | Responses should define whether they can be cached to improve performance. | Add HTTP headers like Cache-Control: max-age=3600. |
| 9. HATEOAS (optional advanced) | API responses can include links to related resources for discoverability. | { "id":1, "name":"Dr. Smith", "_links": {"appointments": "/api/doctors/1/appointments"} } |
| 10. Versioning | Maintain backward compatibility by versioning APIs. | /api/v1/doctors, /api/v2/doctors. |

• Uniform design

| Operation | HTTP Method | Endpoint | Request Body | Description |
| —————— | ————— | —————- | ——————————————————- | ———————— |
| Get all doctors | GET | /api/doctors | — | Retrieve list of doctors |
| Get one doctor | GET | /api/doctors/1 | — | Retrieve specific doctor |
| Create new doctor | POST | /api/doctors | { "name": "Dr. Rao", "specialization": "Cardiology" } | Add a new doctor |
| Update doctor info | PUT | /api/doctors/1 | { "specialization": "Neurology" } | Update doctor details |
| Delete a doctor | DELETE | /api/doctors/1 | — | Remove doctor record |

• To document the REST ful apis there is a standard called as Open API. Generally swagger docs are popular way to document apis

Lets write a fake rest api client in python

• APIs when calling will be of the following categories

  • anonymous/unauthenticated
  • Authenticated
    • Token
    • API Keys

• Look at the following apis

  • https://jsonplaceholder.typicode.com/todos
    • https://jsonplaceholder.typicode.com/todos/1
  • https://jsonplaceholder.typicode.com/users
    • https://jsonplaceholder.typicode.com/users/1
• Create a new project, activate venv and addpackage requests
• and write a simple python code

import requests

BASE_URL = "https://jsonplaceholder.typicode.com"
USERS_URL = f"{BASE_URL}/users"
TODOS_URL = f"{BASE_URL}/todos"


def get_all_users():
    response = requests.get(USERS_URL)
    #print(response)
    users = response.json()
    for user in users:
        print(user['name'])

def make_api_calls():
    get_all_users()



if __name__ == "__main__":
    make_api_calls()

• Refer Here for changes

• Exercise: play around with fake store api and write python functions to perform all operations on product also try aiohttp

Goal: To Create RestAPIs in python

• Gaps:
  • WSGI, ASGI
  • Swagger/OpenApi
  • Defining endpoints
  • Dependency injection
• Next Steps:
  • Authorization & Authentication
  • Testability.
  • Running in a container.