My Flet app works on another Windows PC but not on mine.

[FilipeRuiz]

I developed a Flet app in Python on my Windows 10 PC, with Visual Code and Python 3.12.7. On my PC, the app opens but keeps processing and does not show the elements, such as the buttons and textbox. I copied the same executable and ran it on 3 other computers, which do not have Python installed, and they all opened normally. Does anyone know if there is a security block or something else that could be causing this problem? For testing, I created a new app using the example from the official Flet website, and it also does not work on my PC and worked on another. See the code and the error return in the terminal below.

import asyncio
import sys
if sys.platform == "win32":
    asyncio.set_event_loop_policy(asyncio.WindowsProactorEventLoopPolicy())
import flet as ft
def main(page: ft.Page):
    def add_clicked(e):
        tasks_view.controls.append(ft.Checkbox(label=new_task.value))
        new_task.value = ""
        view.update()
    new_task = ft.TextField(hint_text="What needs to be done?", expand=True)
    tasks_view = ft.Column()
    view=ft.Column(
        width=600,
        controls=[
            ft.Row(
                controls=[
                    new_task,
                    ft.FloatingActionButton(icon=ft.Icons.ADD, on_click=add_clicked),
                ],
            ),
            tasks_view,
        ],
    )

    page.horizontal_alignment = ft.CrossAxisAlignment.CENTER
    page.add(view)

ft.app(main)`

Terminal error

& C:/Users/filip/AppData/Local/Programs/Python/Python312/python.exe d:/Ruiz/07_AppFlet/1_App_Flet_Teste.py
Accept failed on a socket
socket: <asyncio.TransportSocket fd=900, family=2, type=1, proto=0, laddr=('127.0.0.1', 62206)>
Traceback (most recent call last):
File "C:\Users\filip\AppData\Local\Programs\Python\Python312\Lib\asyncio\proactor_events.py", line 846, in loop
conn, addr = f.result()
^^^^^^^^^^
File "C:\Users\filip\AppData\Local\Programs\Python\Python312\Lib\asyncio\windows_events.py", line 803, in _poll
value = callback(transferred, key, ov)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\filip\AppData\Local\Programs\Python\Python312\Lib\asyncio\windows_events.py", line 561, in finish_accept
return conn, conn.getpeername()
^^^^^^^^^^^^^^^^^^
OSError: [WinError 10014] O sistema detectou um endereço de ponteiro inválido ao tentar usar um argumento de ponteiro em uma chamada
Task exception was never retrieved
future: <Task finished name='Task-3' coro=<IocpProactor.accept..accept_coro() done, defined at C:\Users\filip\AppData\Local\Programs\Python\Python312\Lib\asyncio\windows_events.py:563> exception=OSError(14, 'O sistema detectou um endereço de ponteiro inválido ao tentar usar um argumento de ponteiro em uma chamada', None, 10014, None)>
Traceback (most recent call last):
File "C:\Users\filip\AppData\Local\Programs\Python\Python312\Lib\asyncio\windows_events.py", line 566, in accept_coro
await future
OSError: [WinError 10014] O sistema detectou um endereço de ponteiro inválido ao tentar usar um argumento de ponteiro em uma chamada

[ap4499]

An interesting one. It could be a security restriction given the way that Flet uses sockets for communication, especially given it works on other machines. It is hard to say definitively, but given Flet's random socket nature (it finds a random open socket) "Accept failed on a socket" looks like it could be caused by this.

What version of Flet are you on?

flet --version
pip show flet

In the issue above, you mention "executable", have you built your code into a Windows random_application.exe? If so, using Flet Build, or Flet Pack?

Before starting, try disabling any antivirus software and running the app, see if that fixes it, but if not..

Try the following minimal application, while explicitly stating the port:

import flet as ft

def main(page: ft.Page):
    page.add(ft.Text("Hello, Flet!"))

# Run Flet app on a specific port
ft.app(target=main, port=8080)

You might be able to trigger any antivirus / blocking by trying to manually bind / listen to a port:

import socket
import sys


TEST_PORT = 8080 # Or some other port Flet might try. I used the same as the demo app above.

try:
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.bind(('127.0.0.1', TEST_PORT))
        s.listen()
        print(f"Successfully listening on 127.0.0.1:{TEST_PORT}")
        print("Waiting for a connection (Ctrl+C to exit)...")
        conn, addr = s.accept() # This will block until a connection
        with conn:
            print(f"Connected by {addr}")
except OSError as e:
    print(f"Error: Could not bind/listen on port {TEST_PORT}. OS error: {e}")
    sys.exit(1)
except Exception as e:
    print(f"An unexpected error occurred: {e}")
    sys.exit(1)

Does the manual Python script work, but Flet fail?

If that fails, set up a logging/logger to try and see if Flet is giving any useful clues itself.

import logging
import flet as ft
import sys

LOG_FILENAME = 'flet_app.log'
LOG_LEVEL = logging.DEBUG

logging.basicConfig(
    level=LOG_LEVEL,
    format='%(asctime)s - %(levelname)s - %(name)s - [%(threadName)s:%(thread)d] - %(message)s (%(pathname)s:%(lineno)d)',
    filename=LOG_FILENAME,
    filemode='w'
)

logging.info("Logging initialized for Flet app.")

def main(page: ft.Page):
    page.title = "Logging Test App"
    page.add(ft.Text("Hello, Flet with logging!"))
    logging.debug("Main page loaded.")

if __name__ == "__main__":
    ft.app(
        target=main,
        logging_level=logging.DEBUG
    )

[FilipeRuiz]

Hello Alex.

May configuration:
Flet version 0.28.2
Python 3.10
Windows 10 Home
Intel Core i5-10210U

Sorry for the delay in responding. I did the tests you indicated above, and I would like to take this opportunity to thank you for your help, but it did not solve the problem. After much research and tests by acquiring the logs you indicated, I found the error in Windows Winsock (Sockets). I was able to find it by uploading the logs and configuration of my computer to the gpt chat. He gave me the following analysis:

Winsock (Sockets) failure – The logs provided indicate a socket error in the asyncio loop: WinError 10014 – “The system detected an invalid pointer address…” when trying to accept connections in the loopback (127.0.0.1). This error is a known bug in Windows that corrupts the network library (Winsock) and prevents local TCP connections. Similar reports have occurred in other apps (e.g. Stable Diffusion WebUI), and the cause is usually a Winsock configuration corrupted by updates or network software. The typical symptom is exactly this “Accept failed on a socket… WinError 10014”, resulting in an unreachable local server and a black screen in the app.

Diagnostic Steps and Suggested Fixes
Reset the Winsock Stack: The first and most reliable step is to fix the Winsock error that appears in the logs. Run in the Command Prompt (CMD) as Administrator:

netsh winsock reset

Then, restart the computer. This command restores the default Windows Winsock configuration. Several cases have reported that this immediately resolves the WinError 10014 error and restores local TCP connections. For example, a user with the same error in asyncio reported: “I ran netsh winsock reset as admin, restarted the PC and the webUI application started working again” github.com. This procedure should eliminate the root cause of the black screen (which was the local Flet server not accepting connections). Checking Sockets Operation Locally: After the Winsock reset, test the Flet app again. If it still doesn't work, perform some manual tests:

Open a Python terminal and try to create a simple socket listening on 127.0.0.1 to see if there is still an error. For example:

import socket; s=socket.socket(); s.bind(('127.0.0.1', 0)); s.listen()

If this generates an error immediately, there is still a local network problem in Windows.

Also try accessing the address and port that Flet indicates in the logs (e.g.: 127.0.0.1:50263) via browser. See if anything different happens or if there is an error message in the browser.

After the reset, all the applications that I had created on this computer and others worked. I turned the firewall and antivirus back on and everything is ok.

Thank you very much for your help and I hope this content can help more people. Best regards.

This is the last teste code running.

import logging
import sys
import asyncio
import flet as ft

LOG_FILENAME = 'flet_app.log'
LOG_LEVEL = logging.DEBUG

logging.basicConfig(
    level=LOG_LEVEL,
    format='%(asctime)s - %(levelname)s - %(name)s - [%(threadName)s:%(thread)d] - %(message)s (%(pathname)s:%(lineno)d)',
    filename=LOG_FILENAME,
    filemode='w'
)

logging.info("Logging initialized for Flet app.")

def main(page: ft.Page):
    page.title = "Logging Test App"

    input_field = ft.TextField(label="Digite algo")
    output_text = ft.Text(value="", size=40)

    def on_button_click(e):
        logging.debug(f"Texto digitado: {input_field.value}")
        output_text.value = f"Você digitou: {input_field.value}"
        page.update()

    button = ft.ElevatedButton(text="Enviar", on_click=on_button_click)

    page.add(
        ft.Column(
            controls=[
                ft.Text("Hello, Flet with logging!"),
                input_field,
                button,
                output_text
            ],
            spacing=20
        )
    )

# CODE TO RUN WINDOWS APPLICATION
#if __name__ == "__main__":    ft.app(target=main)

#CODE TO RUN WEB MODE APPLICATION
ft.app(target=main, view=ft.WEB_BROWSER, web_renderer=ft.WebRenderer.CANVAS_KIT)
 

[ap4499]

did you find the solution to this?