from serial import Serial
import threading
from fastapi import FastAPI

s=""

ser = Serial('COM4', 9600)
def pot():
    global s
    while True:  
        s = ser.read(1)       # read up to one hundred bytes
th=threading.Thread(target=pot)
th.start()
app = FastAPI()

@app.get("/")
async def root():
    return ("message", s)