How to prevent uv with a tkinter application giving xcb error

Question

I am using uv to manage my python environments and I am getting a low level error message when I try to run a simple tkinter script

#   xxx.py    
import tkinter as tk

def main():
    root = tk.Tk()
  
    label = tk.Label(root, text="This line causes the problem")
    label.pack()
    root.mainloop()

 if __name__ == "__main__":
    main()

When I run the code using

uv run xxx.py

I get an error message

    ➜ uv run xxx.py             
    Using CPython 3.13.6
    Creating virtual environment at: .venv
    [xcb] Unknown sequence number while appending request
    [xcb] You called XInitThreads, this is not your fault
    [xcb] Aborting, sorry about that.
    python: xcb_io.c:157: append_pending_request: Assertion `!xcb_xlib_unknown_seq_number' failed.

I am NOT using threading!

My system is:

Operating System: Manjaro Linux 
KDE Plasma Version: 6.3.6
KDE Frameworks Version: 6.17.0
Qt Version: 6.9.1
Kernel Version: 6.6.90-1-MANJARO (64-bit)
Graphics Platform: X11
Processors: 20 × 13th Gen Intel® Core™ i5-13500
Memory: 62.5 GiB of RAM

lspci | grep VGA

01:00.0 VGA compatible controller: NVIDIA Corporation AD106 [GeForce RTX 4060 Ti 16GB] (rev a1)

I cannot fathom the problem

Petr Raska · Accepted Answer · 2025-09-24 09:31:53Z

3

There was recently bug in the uv, it should be solved, but you can have the buggy version on your system.

uv self update
uv python upgrade --reinstall

#clear local .venv if exists
rm -rf .venv

Now you should be able to just run:

uv run xxx.py

or with any particular version you like:

uv run -p 3.13.6 xxx.py

edited Sep 24 at 9:31

answered Sep 24 at 9:29

Petr Raska

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1 Comment

Psionman Sep 25 at 10:09

NB uv and tkinter have some unresolved issues as of now (25 Sept 2025) see this bug report

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