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author Margit ANTAL
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Module 2: Getting Started with FastAPI

🚀 Overview

  • FastAPI project structure
  • Creating GET API endpoints
  • Path and query parameters
  • Pydantic models
  • Creating POST API endpoints
  • Standard logging

Why FastAPI?

  • High performance, built on Starlette and Pydantic
  • Automatic data validation and type checking
  • Automatic API docs (Swagger & Redoc)
  • First-class support for async and await
  • FastAPI = Starlette (web) + Pydantic (data)

Pydantic Examples (1)

from pydantic import BaseModel, ValidationError

class User(BaseModel):
    name: str
    age: int
    email: str | None = None

try:
    u = User(name="Alice", age="34", email="alice@example.com")
    print(u)
except ValidationError as e:
    print(e)

Pydantic Examples (2)

Loading configuration from JSON file (config.json):

{
  "host": "localhost",
  "port": 8080,
  "debug": true
}

Pydantic Examples (2) (cont)

from pydantic import BaseModel
import json

class Config(BaseModel):
    host: str
    port: int
    debug: bool

with open("config.json") as f:
    data = json.load(f)

config = Config(**data)
print(config.port)

FastAPI Project Structure

Common structure:

  • main.py – entry point
  • routers/ – modular routes
  • models/ – Pydantic or DB models
  • services/ – business logic
  • config.py – env variables, settings

Creating Your First Endpoint

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello, FastAPI"}

Running FastAPI with Uvicorn

Install:

pip install fastapi uvicorn

Run the app:

uvicorn main:app --reload
  • --reload enables auto-reload on file changes

Pydantic model

from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: float
    in_stock: bool = True
items: list = list(
    Item(
        name="Sample Item " + str(i+1), 
        price=(i+1) * 10.0, 
        in_stock=True) 
    for i in range(10))

Path Parameters

Define variables in the URL:

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

Examples:

curl http://localhost:8000/items/2
# → {"item_id": 2}

curl http://localhost:8000/items
# → 404 Not Found

Query Parameters

Optional inputs:

@app.get("/items/")
def read_item(skip: int = 0, limit: int = 10):
    return {"skip": skip, "limit": limit}

Examples:

curl http://localhost:8000/items/
# → {"skip": 0, "limit": 10}

Examples (cont):

curl 'http://localhost:8000/items/?skip=5&limit=3'
# → {"skip": 5, "limit": 3}

curl 'http://localhost:8000/items/?skip=5'
# → {"skip": 5, "limit": 10}

curl 'http://localhost:8000/items/?limit=3'
# → {"skip": 0, "limit": 3}

Path vs Query Parameters

Path Parameters Query Parameters
Part of the URL Appended after ?
Required Optional (default values)
Used to identify resource Used for filtering, pagination

Using Pydantic Models

from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: float
    in_stock: bool = True

Creating POST Endpoints with Pydantic

items = list()

@app.post("/items/")
def create_item(item: Item):
    items.append(item)
    return {"item_name": item.name, "price": item.price}
  • Example:
curl -X POST "http://localhost:8000/items/" \
     -H "Content-Type: application/json" \
     -d '{"name": "Book", "price": 12.99}'

Standard Logging

import logging
from fastapi import FastAPI

app = FastAPI()

logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s - %(name)s - %(levelname)s - %(message)s"
)
logger = logging.getLogger("myapp")

@app.get("/")
def read_root():
    logger.info("Root endpoint was called")
    return {"Hello": "World"}

FastAPI Docs Interface

FastAPI auto-generates API docs:

Homework

Link to homework Section: Practical Exercises: Item Management API

🎯 Remember

  • FastAPI project structure
  • GET endpoints
  • Path parameters
  • Query parameters
  • Pydantic request/response models
  • POST endpoints
  • OpenAPI/Swagger documentation