# FastAPI: A Modern Python Web Framework

## What is FastAPI?

FastAPI is a modern, high-performance web framework for building APIs with Python 3.6+ that's gaining massive popularity. Think of it as the "Formula 1 car" of Python web frameworks - it's incredibly fast and packed with features.

## Key Features That Make FastAPI Special

### 🚀 **Blazing Fast Performance**
- Built on **Starlette** (for web) and **Pydantic** (for data)
- Comparable to Node.js and Go in speed
- One of the fastest Python frameworks available

### 📝 **Type Hints Power**

from typing import Optional
from fastapi import FastAPI
from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: float
    is_offer: Optional[bool] = None

app = FastAPI()

@app.post("/items/")
def create_item(item: Item):  # Type hints = automatic validation!
    return item

### 📚 **Automatic API Documentation**
- **Swagger UI** at `/docs`
- **ReDoc** at `/redoc`
- Both generated automatically from your code!

## Let's Build Something Real

### Installation

pip install fastapi uvicorn

### Basic Example - E-commerce API

from fastapi import FastAPI, HTTPException
from pydantic import BaseModel
from typing import List, Optional
from uuid import UUID, uuid4

app = FastAPI(title="E-Commerce API", version="1.0.0")

# Data models
class Product(BaseModel):
    id: UUID
    name: str
    price: float
    in_stock: bool = True

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

# In-memory "database"
products: List[Product] = []

# Routes
@app.get("/")
async def root():
    return {"message": "Welcome to our E-Commerce API!"}

@app.get("/products", response_model=List[Product])
async def get_products():
    return products

@app.get("/products/{product_id}")
async def get_product(product_id: UUID):
    for product in products:
        if product.id == product_id:
            return product
    raise HTTPException(status_code=404, detail="Product not found")

@app.post("/products", response_model=Product)
async def create_product(product_request: CreateProductRequest):
    product = Product(
        id=uuid4(),
        name=product_request.name,
        price=product_request.price,
        in_stock=product_request.in_stock
    )
    products.append(product)
    return product

@app.put("/products/{product_id}")
async def update_product(product_id: UUID, updated_product: CreateProductRequest):
    for idx, product in enumerate(products):
        if product.id == product_id:
            products[idx] = Product(
                id=product_id,
                name=updated_product.name,
                price=updated_product.price,
                in_stock=updated_product.in_stock
            )
            return products[idx]
    raise HTTPException(status_code=404, detail="Product not found")

@app.delete("/products/{product_id}")
async def delete_product(product_id: UUID):
    for idx, product in enumerate(products):
        if product.id == product_id:
            return products.pop(idx)
    raise HTTPException(status_code=404, detail="Product not found")

### Running the Server

uvicorn main:app --reload

Visit:
- **API**: http://localhost:8000
- **Docs**: http://localhost:8000/docs
- **Alternative Docs**: http://localhost:8000/redoc

## Advanced Features

### Query Parameters & Validation

from fastapi import Query

@app.get("/products/")
async def search_products(
    name: Optional[str] = Query(None, min_length=2, max_length=50),
    min_price: Optional[float] = Query(0, ge=0),
    max_price: Optional[float] = Query(1000, le=10000),
    in_stock: bool = True
):
    # Your filtering logic here
    return {"filters": {"name": name, "min_price": min_price}}

### Dependency Injection

from fastapi import Depends

async def get_database():
    # Simulate database connection
    return {"db": "connected"}

@app.get("/users/")
async def read_users(db: dict = Depends(get_database)):
    return {"users": ["Alice", "Bob"], "database_status": db}

### Background Tasks

from fastapi import BackgroundTasks

def send_order_confirmation_email(order_id: UUID):
    # Simulate email sending
    print(f"Sent confirmation for order {order_id}")

@app.post("/orders/")
async def create_order(
    background_tasks: BackgroundTasks,
    product_id: UUID
):
    order_id = uuid4()
    background_tasks.add_task(send_order_confirmation_email, order_id)
    return {"order_id": order_id, "status": "created"}

## Real-World Project Structure

my_ecommerce_api/
├── main.py
├── routers/
│   ├── products.py
│   ├── users.py
│   └── orders.py
├── models/
│   ├── product.py
│   └── user.py
├── dependencies.py
└── database.py

## Why Developers Love FastAPI

### ✅ **Advantages**
- **Rapid Development**: Write less code, get more features
- **Fewer Bugs**: Type checking catches errors early
- **Great Editor Support**: Autocompletion everywhere
- **Modern Python**: Uses latest Python features
- **Easy to Learn**: Intuitive and well-documented

### 🎯 **Perfect Use Cases**
- RESTful APIs
- Microservices
- Internal tools
- Prototyping
- Machine Learning APIs

## Performance Comparison

Framework        Requests/sec
FastAPI          ~10,000
Flask            ~2,000
Django           ~1,500
Node.js Express  ~8,000

## Quick Tips for Success

1. **Use type hints religiously** - they're your superpower
2. **Leverage automatic docs** - your API is self-documenting
3. **Use dependencies** for database connections, authentication
4. **Test with the built-in TestClient**
5. **Deploy with Uvicorn** in production

## Example: Testing Your API

from fastapi.testclient import TestClient
from main import app

client = TestClient(app)

def test_create_product():
    response = client.post(
        "/products/",
        json={"name": "Laptop", "price": 999.99}
    )
    assert response.status_code == 200
    assert response.json()["name"] == "Laptop"

FastAPI feels like magic because it turns Python's type hints into a powerful development experience. You get validation, serialization, documentation, and editor support almost for free!

The framework is particularly excellent for:
- Building production-ready APIs quickly
- Teams that want maintainable, self-documenting code
- Projects that need high performance
- Developers who love modern Python features