FastAPI Handwritten Notes PDF Download | Complete FastAPI Notes for Beginners

FastAPI is a modern, fast (high-performance) web framework for building APIs with Python 3.7+ based on standard Python type hints. It is designed for ease of use, automatic data validation, and excellent performance (comparable to Node and Go frameworks). These handwritten notes summarize essential FastAPI concepts in a concise, exam- and interview-friendly format.

Installation & Setup

Install FastAPI and an ASGI server (Uvicorn) using pip:

pip install fastapi uvicorn

Run the app with Uvicorn:

uvicorn app:app --reload

Basics: Routes & Path Operations

FastAPI uses path operation decorators to define routes. Example:

from fastapi import FastAPI

app = FastAPI()

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

Supported methods: @app.get, @app.post, @app.put, @app.delete, @app.patch.

Pydantic Models & Validation

FastAPI uses Pydantic for data validation and settings management. Define request bodies using Pydantic models:

from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None

Pydantic automatically validates and converts data types from JSON requests.

Path, Query & Request Body

Examples of different parameter types:

@app.get("/items/{item_id}")
async def read_item(item_id: int, q: str | None = None):
    return {"item_id": item_id, "q": q}

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

Use type hints for automatic parsing and validation. Default values make query params optional.

Dependency Injection

FastAPI provides a simple and powerful dependency injection system for reusing logic (e.g., DB sessions, authentication):

from fastapi import Depends

def get_db():
    db = connect_db()
    try:
        yield db
    finally:
        db.close()

@app.get("/users/")
async def list_users(db = Depends(get_db)):
    return db.query_users()

Background Tasks & Events

Run non-blocking background work using BackgroundTasks or startup/shutdown events:

from fastapi import BackgroundTasks

def write_log(message: str):
    with open("log.txt", "a") as f:
        f.write(message)

@app.post("/send/")
async def send_message(background_tasks: BackgroundTasks, msg: str):
    background_tasks.add_task(write_log, msg)
    return {"status": "queued"}

Middleware & CORS

Use middleware for request/response processing and configure CORS for cross-origin requests:

from fastapi.middleware.cors import CORSMiddleware

app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_methods=["*"],
    allow_headers=["*"],
)

Authentication & Security

FastAPI supports OAuth2, JWT, API keys, and HTTP Basic auth. Example using OAuth2PasswordBearer:

from fastapi.security import OAuth2PasswordBearer

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

@app.get("/users/me")
async def read_users_me(token: str = Depends(oauth2_scheme)):
    return {"token": token}

Always validate tokens, use HTTPS in production, and follow security best practices.

Testing FastAPI Apps

Use TestClient from starlette.testclient (or FastAPI's built-in wrapper) with pytest:

from fastapi.testclient import TestClient

client = TestClient(app)

def test_read_root():
    response = client.get("/")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello FastAPI"}

Deployment Tips

• Use a production ASGI server (Uvicorn/Gunicorn with workers): gunicorn -k uvicorn.workers.UvicornWorker app:app
• Containerize with Docker for consistent environments.
• Use process managers and monitoring (systemd, supervisord, or Kubernetes).
• Configure logging, metrics, and health checks.

Example: Simple CRUD App

from fastapi import FastAPI, HTTPException
from pydantic import BaseModel
from typing import Dict

app = FastAPI()
db: Dict[int, dict] = {}
next_id = 1

class Item(BaseModel):
    name: str
    description: str | None = None

@app.post("/items/", status_code=201)
async def create_item(item: Item):
    global next_id
    item_data = item.dict()
    db[next_id] = item_data
    next_id += 1
    return {"id": next_id - 1, **item_data}

@app.get("/items/{item_id}")
async def get_item(item_id: int):
    if item_id not in db:
        raise HTTPException(status_code=404, detail="Item not found")
    return db[item_id]

Study Tips & How to Use These Notes

• Read the notes while running sample code — FastAPI is best learned by doing.
• Start with synchronous examples, then move to async endpoints and concurrency patterns.
• Practice building small projects (auth API, task queue, microservice).
• Use the notes as a quick reference during interviews.

FAQ

Who is this PDF for?

These notes are for Python developers, backend learners, and anyone preparing for API development interviews.

Is the PDF free?

Yes - replace the download link above with your hosted PDF URL to offer a free download.

Do these notes cover async programming?

Yes - the PDF includes explanations and examples of asynchronous endpoints, concurrency, and background tasks.