"Hello world" tkinter app with a fastapi backend

tkfront.py

import tkinter, fastapi
import requests

port = 8003

localurl = f"http://localhost:{port}/"

def uimain():
    def doit():
        endpoint = "transform/"
        xis = requests.get(localurl + endpoint, params={"text":entryvar.get()})
        outvar.set(xis.json()["text"])
        
    window = tkinter.Tk()
    text = tkinter.Entry(window, textvariable=(entryvar:=tkinter.Variable()) )
    label = tkinter.Label(window, textvariable=(outvar:=tkinter.Variable()) )
    button = tkinter.Button(window, text="ok", command=doit)
    for widget in (text, label, button):
        widget.pack()
    tkinter.mainloop()

def backmain():
    global app
    app = fastapi.FastAPI()

    @app.get("/transform/")
    async def transform(text: str):
        return {"text": text.upper() * 2}

if __name__ == "__main__":
    import os, subprocess
    if not (pid:=os.fork()):
        fastapi = subprocess.Popen(["fastapi", "run", "--port", str(port), __file__])
        open("tkfront.pid", "wt").write(str(fastapi.pid))
        fastapi.wait()
        exit(0)
    try:
        uimain()
    finally:
        os.system(f"kill {open('tkfront.pid').read()}")
        os.unlink("tkfront.pid")
else:
    backmain()