Overview

FastAPI is a modern, fast web framework for building APIs with Python. It can provide high performance on par with Node.js and Go.

Starlette & Uvicorn

Both Starlette and Uvicorn are essential components in the FastAPI ecosystem.

Starlette

• starlette is a lightweight ASGI (Async Server Gateway Interface) framework for building web apps
• FastAPI is built on top of starlette and pydantic, and it abstracts most of the complexity of starlette
• starlette provides core functionality for handling web requests, responses, routing, middleware and more.

Uvicorn:

• uvicorn is an ASGI server implementation, desgined to run ASGI applications, like the ones built with starlette and fastapi
• after you build your own fastapi application, you can run it with uvicorn main:app --reload

Start FastAPI Server

To start the application:

uvicorn run demo.main:app --reload

Here, demo is the project, main.py is the main file and app is an instance of FastAPI().

To view the Swagger.io endpoint http://127.0.0.1:8000/docs.

Entry Point

Let’s define the main entry point of the api:

# demo/main.py
import uvicorn
from fastapi import FastAPI

app = FastAPI()

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

def start():
    uvicorn.run("app.main:app", host="127.0.0.1", port=8000, reload=True)

API Routers

Let’s define a router:

# demo/routers/user.py
from fastapi import APIRouter

router = APIRouter()

@router.post("/parse", response_model=ParserResponse)
async def parse(req: ParserRequest):
    return {"message": "parse done"}

Then include the router:

# demo/main.py
from app.routers import parser

app.include_router(parser.router)

Upload Files

Install python-multipart, that’s a dependency.

@router.post("/parse")
async def parse(source_tempate: UploadFile = File(...), parameters: UploadFile = File(...)):
    pass