FastAPI leverages asynchronous programming to provide high-performance web applications and APIs. Asynchronous programming allows tasks to be executed concurrently without waiting for each to complete, making better use of system resources and improving overall application responsiveness. Here are some key aspects of the asynchronous features in FastAPI:

Async and Await Syntax : FastAPI uses Python's async and await syntax to define asynchronous functions. These functions can be used in route handlers, dependencies, and other parts of the application.

from fastapi import FastAPI

app = FastAPI()

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

Asynchronous Request Handlers : FastAPI allows you to define asynchronous request handlers using the async def syntax. This is particularly useful for handling requests concurrently, especially when dealing with I/O-bound operations such as database queries or external API calls.

from fastapi import FastAPI

app = FastAPI()

@app.get("/async_endpoint")
async def async_endpoint():
    result = await some_async_function()
    return {"result": result}?

Dependency Injection with Async Dependencies : FastAPI's dependency injection system supports asynchronous dependencies. Dependencies marked with async def can perform asynchronous operations, such as fetching data from a database or making asynchronous API calls.

from fastapi import Depends, FastAPI

app = FastAPI()

async def get_some_data():
    # Asynchronous operations here
    return {"data": "Some asynchronous data"}

@app.get("/")
async def read_data(data: dict = Depends(get_some_data)):
    return data?

Background Tasks : FastAPI provides a mechanism called BackgroundTasks that allows you to run asynchronous functions in the background after a response has been sent to the client. This is useful for performing non-blocking tasks after handling a request.

from fastapi import BackgroundTasks, FastAPI

app = FastAPI()

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

@app.post("/send-notification/{email}")
async def send_notification(
    email: str, background_tasks: BackgroundTasks
):
    message = f"message to {email}"
    background_tasks.add_task(write_log, message)
    return {"message": "Message sent in the background"}?

WebSocket Support : FastAPI supports asynchronous WebSocket communication. You can define WebSocket routes using asynchronous functions, enabling real-time bidirectional communication between clients and the server.

from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(f"Message text was: {data}")

By embracing asynchronous programming, FastAPI is able to handle a large number of simultaneous connections efficiently, making it suitable for building scalable and performant web applications and APIs.