Why WebSockets enable real-time communication in FastAPI

Introduction

WebSockets let your app talk back and forth instantly without waiting. This makes real-time updates possible, like chat or live scores.

Building a chat app where messages appear instantly

Showing live sports scores or stock prices that update continuously

Creating multiplayer games where players see each other's moves right away

Implementing notifications that pop up immediately when something happens

Streaming live data like GPS locations or sensor readings

Syntax

FastAPI

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}")

Use @app.websocket to create a WebSocket route.

Call await websocket.accept() to start the connection.

Examples

Accepts the WebSocket connection from the client.

FastAPI

await websocket.accept()

Waits to receive a text message from the client.

FastAPI

data = await websocket.receive_text()

Sends a text message back to the client.

FastAPI

await websocket.send_text(f"Echo: {data}")

Sample Program

This FastAPI app opens a WebSocket at /ws. When a client connects and sends a message, the server replies immediately with the same message prefixed by 'You said:'. This shows real-time two-way communication.

FastAPI

from fastapi import FastAPI, WebSocket
import uvicorn

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"You said: {data}")

if __name__ == "__main__":
    uvicorn.run(app, host="127.0.0.1", port=8000)

Important Notes

WebSockets keep the connection open, unlike normal HTTP requests that close after response.

This makes WebSockets perfect for live updates without repeated requests.

Remember to handle connection closing and errors in real apps.

Summary

WebSockets allow instant two-way communication between client and server.

FastAPI supports WebSockets with simple async functions and decorators.

This enables real-time features like chat, live data, and notifications.