fastapi

FastAPI

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.8+ based on standard Python type hints. It is one of the fastest Python frameworks available.

When to Use

• High-Performance Python Web APIs: Developing modern async APIs built on Starlette and Pydantic.
• AI & Machine Learning Model Serving: Serving PyTorch, TensorFlow, Scikit-learn, and Hugging Face inference endpoints.
• Automatic OpenAPI & Swagger Documentation: Generating interactive documentation with zero manual configuration.
• Data Validation & Type-Safe Payloads: Validating query parameters, paths, headers, and request bodies with Pydantic v2.

Quick Start

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float

@app.post("/items/")
async def create_item(item: Item):
    return {"name": item.name, "price": item.price}

Core Concepts

Async Route Handlers & Pydantic v2 Models

Strict payload parsing and serialization:

from fastapi import FastAPI, HTTPException, status, Depends
from pydantic import BaseModel, EmailStr, Field
from typing import List

app = FastAPI(title="Catalog API", version="2.0.0")

class ProductCreate(BaseModel):
    name: str = Field(min_length=2, max_length=100)
    price: float = Field(gt=0, description="Price in USD")
    tags: List[str] = []

class ProductResponse(ProductCreate):
    id: int
    is_active: bool = True

@app.post("/products", response_model=ProductResponse, status_code=status.HTTP_201_CREATED)
async def create_product(product: ProductCreate):
    # Process and persist product
    return {
        "id": 101,
        "name": product.name,
        "price": product.price,
        "tags": product.tags,
        "is_active": True
    }

Dependency Injection System with Depends

Reusing database sessions, authentication, and service clients:

from fastapi import Header, HTTPException

async def verify_api_key(x_api_key: str = Header(...)):
    if x_api_key != "secret-internal-key":
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="Invalid API Key"
        )
    return x_api_key

@app.get("/secure-metrics")
async def get_metrics(api_key: str = Depends(verify_api_key)):
    return {"status": "authorized", "system_load": 0.42}