main.py

import requests
from yeelight import Bulb
from concurrent.futures import ThreadPoolExecutor
from fastapi import FastAPI


app = FastAPI()

@app.get("/")
async def read_root():
    """IFTTT variant: takes about 3 seconds after the switch is toggled to toggle lights.
    Unfortunately, Shelly cannot reach external IP addresses for some reason, then there wouldn't
    be a need for this server :-(
    """
    requests.get("https://maker.ifttt.com/trigger/bedroom_switch/with/key/XXX")
    return "ok"

def toggle_bulb(bulb: Bulb):
    return bulb.toggle()

@app.get("/yl")
async def yeelight():
    """Is close to immediate"""
    a = Bulb("192.168.0.172")  # you have to change these to your bulb addresses
    b = Bulb("192.168.0.136")
    with ThreadPoolExecutor(2) as executor:  # just to switch them concurrently
        res = executor.map(toggle_bulb, [a, b])
    return res

The way to run it on e.g. 192.168.0.121

sudo uvicorn --reload main:app --port 80 --host 192.168.0.121