Week 2

Week 2

Join the github classroom assignment with the following link: 

Once you join your repository will be created https://github.com/blueprint-learn/week2-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

Recap last week

• We built a running FastAPI server

• We created endpoints

• We used path parameters

• CI tested our API contract

Goal for today

By the end of today, you will understand how APIs receive structured data and how FastAPI validates it automatically.

Big idea

Last week: Client asks for data

This week: Client sends data

1. How Data Enters an API

There are three main ways data reaches an API:

Path parameters

/items/5

Query parameters

/items?limit=10

Request body (JSON)

Type	Where used	Example
Path	Identify resource	/users/3
Query	Filter/search	?limit=10
Body	Send data	POST JSON

2. Query Parameters

@app.get("/items")
def list_items(limit: int = 10):
    return {"limit": limit}

Show

• /items

• /items?limit=5

• /items?limit=abc

Explain

• Default values

• Type conversion

• Automatic validation

Key insight

FastAPI parses query strings into typed Python values.

3. Request Bodies & JSON

Motivation

Real APIs receive structured data:

• User signup

• Orders

• Messages

• Payments

Example request

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

Naive version

@app.post("/items")
def create_item(item: dict):
    return item

Problem

• No validation

• No structure

• No guarantees