Week 1

Week 1

Join the github classroom assignment with the following link: https://classroom.github.com/a/KOc7f0j5

Once you join your repository will be created https://github.com/blueprint-learn/week1-techteam-sp26-{github-username}

You will get an email with access to your repo

Clone your repo

git clone https://github.com/blueprint-learn/week1-techteam-sp26-{github-username}.git

Goal for today

By the end of this class, you will understand what an API is and you will have written and run a real backend service.

Set expectations

• This is not web dev with HTML

• This is backend infrastructure

• What we build today looks simple, but it’s the same pattern used by Netflix, Stripe, AWS, etc.

1. What Is an API? 

Core idea

• API = contract between a client and a server

• You ask for data → server responds with data

Client (browser / app / script)
        |
        |  HTTP request
        v
      API Server
        |
        |  JSON response
        v
      Client

Key clarification

• APIs don’t care who the client is

• Browser, mobile app, another server — all the same

Examples 

• Instagram feed

• Spotify playlists

• Google Maps directions

2. REST & HTTP Basics

REST (high-level)

• Everything is a resource

• Each resource has a URL

HTTP Methods

Method	Meaning
GET	Read data
POST	Create data
PUT	Update data
DELETE	Remove data

HTTP Response

• Status code (200, 404, etc.)

• Body (usually JSON)

{
  "id": 3,
  "name": "Notebook",
  "price": 5.99
}

Important

• JSON ≠ Python dictionary (but very similar)

3. Live Demo Setup

pip3 install -r requirements.txt

Minimal app

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def root():
    return {"message": "Hello World"}

Run the app

uvicorn app.main:app --reload

4. Endpoints & Path Parameters

@app.get("/items/{item_id}")
def read_item(item_id: int):
    return {"item_id": item_id}

• Automatic validation
• Type validation