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How can you create a REST API with FastAPI in Python?

Anubhav Sharma 2220 06 Nov 2025

How can you create a REST API with FastAPI in Python?

1 Answers

ICSM Computer 24 Nov 2025

Creating a REST API with FastAPI in Python is simple, fast, and production-ready. Below is a clean step-by-step guide.

Step 1 — Install FastAPI & Uvicorn

pip install fastapi uvicorn

Step 2 — Create an API file

Create a file named main.py:

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Welcome to FastAPI!"}

@app.get("/hello/{name}")
def say_hello(name: str):
    return {"message": f"Hello, {name}"}

Step 3 — Run the API server

uvicorn main:app --reload

main → filename (main.py)
app → FastAPI instance
--reload → auto-reload on code changes (useful during development)

Example CRUD REST API

Below is a complete example for managing items in memory.

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

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

items = {}

@app.post("/items/{item_id}")
def create_item(item_id: int, item: Item):
    items[item_id] = item
    return {"message": "Item created", "item": item}

@app.get("/items/{item_id}")
def get_item(item_id: int):
    return items.get(item_id, {"error": "Item not found"})

@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):
    items[item_id] = item
    return {"message": "Item updated", "item": item}

@app.delete("/items/{item_id}")
def delete_item(item_id: int):
    items.pop(item_id, None)
    return {"message": "Item deleted"}

Test the API

After running uvicorn, open your browser:

http://127.0.0.1:8000/docs → FastAPI’s Swagger UI
http://127.0.0.1:8000/redoc → Alternative documentation view

FastAPI auto-generates documentation using OpenAPI — no extra code needed.

Adding CORS (optional — for frontend apps)

from fastapi.middleware.cors import CORSMiddleware

app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],  # list specific domains in production
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

With Database Example (SQLAlchemy)

Install DB dependencies first:

pip install sqlalchemy

Sample setup:

from fastapi import FastAPI, Depends
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

DATABASE_URL = "sqlite:///./test.db"
engine = create_engine(DATABASE_URL)
SessionLocal = sessionmaker(bind=engine)

app = FastAPI()

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

This allows injecting DB sessions into your routes.

Why FastAPI?

Feature	Benefit
Very Fast	Built on ASGI + Starlette
Auto Docs	Swagger & ReDoc
Pydantic Models	Validation + Serialization
Async Ready	Supports `async`/`await`
Production Friendly	Works well with Docker, Gunicorn, Kubernetes

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