SyntaxError: Non-UTF-8 code starting with '\x90' in file python.exe on line 1, but no encoding declared.

[jovan2009]

Hi, use Python 3.13.9 downloaded from this repository. I downloaded the file named cpython-3.13.9+20251031-x86_64-pc-windows-msvc-pgo-full.tar.zst. I unzipped it in a folder and I set this environment variables in addition to adding it to the PATH:

It is in fact copied with overwrite over an older installation of python that I downloaded from the same repository several weeks ago and unzipped in the same manner I mentioned.

I noticed recently that when I start python.exe with no arguments in command prompt I get before anything else an error message:

Microsoft Windows [Version 10.0.26200.7019]
(c) Microsoft Corporation. All rights reserved.

C:\Users\Sidef>C:\Python313\install\python.exe
Python 3.13.9 (main, Oct 31 2025, 22:58:20) [MSC v.1944 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
SyntaxError: Non-UTF-8 code starting with '\x90' in file C:\Python313\install\python.exe on line 1, but no encoding declared; see https://peps.python.org/pep-0263/ for details
Failed calling sys.__interactivehook__
Traceback (most recent call last):
  File "<frozen site>", line 536, in register_readline
AttributeError: module 'readline' has no attribute 'backend'
>>>

I don't encounter (or it's not obvious to me) any particular problem when I use it for my main purpose, to run ComfyUI. I just wanted to let you know what's happening. I'm not a developer and I don't understand the meaning of the error, the cause or what might imply.

[jjhelmus]

The issue here is that PYTHONSTARTUP is set to the interpreter which is a binary file.

The PYTHONSTARTUP environment variable is used to specify python commands which are executed before an interactive prompt is shows. The variable does not need to be set and often is not. If it is set it should specify a text file with Python commands, not the interpreter.

[jovan2009]

@jjhelmus
Thanks a lot for your answer. I obviously didn't know what I am doing. I eliminated all the mentioned environment variables (PYTHONSTARTUP but also the other 2 since I don't know what they are doing either or if they are needed). Python.exe is still in PATH so I can run it from any folder. Indeed the error does not show up any more but it still seems to complain about something. Probably with no perceivable consequences, at least from what I can tell, during regular use. Might be my own fault, since I originally installed an older 3.13 build a while ago (from the same repository) and I "updated" it by simply overwriting the content of the folder with the latest similar build (in terms of python version and operating system), maybe that's not the right way to do such thing.

Microsoft Windows [Version 10.0.26200.7171]
(c) Microsoft Corporation. All rights reserved.

C:\Users\Sidef\Desktop>python
Python 3.13.9 (main, Oct 31 2025, 22:58:20) [MSC v.1944 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
Failed calling sys.__interactivehook__
Traceback (most recent call last):
  File "<frozen site>", line 536, in register_readline
AttributeError: module 'readline' has no attribute 'backend'
>>>