Python 3.12.1, Windows 11: shebang line #!/usr/bin/env python3 doesn't work any more

[Thomas Passin]

On 1/1/2024 6:02 AM, Sibylle Koczian via Python-list wrote:
> Am 30.12.2023 um 04:04 schrieb Mike Dewhirst via Python-list:
>>
>> I had assumed the OP had installed Python from the Microsoft shop and 
>> that's where py.exe must have come from.
>>
> 
> In fact I didn't say in my post that I always get Python from 
> python.org. When I started to use the language there was no Python from 
> any Microsoft shop (I'm not sure there was a Microsoft shop, it was in 
> the last millenium, Python 1.5 or 1.6). So I tend to forget that 
> possible download source.
> 
> But in all this thread I didn't see a single explanation for my current 
> situation: one and the same shebang line works on Windows 10 / Python 
> 3.11 and doesn't work on Windows 11 / Python 3.12. I suspect Windows, 
> because a change in the way Python 3.12 uses shebang lines should be 
> visible in the documentation.
> 
> Happy new year to all!
> Sibylle

Happy New Year!

I speculated that the shebang line didn't work on Windows 10 either, but 
you didn't realize it because the file associations were right to launch 
".py" programs with the right version of Python.  When the newer version 
of Python got installed, the default Python program to use, was not 
updated correctly, and the shebang line still has nothing to do with the 
launch failure.  This could happen if other the older install went into 
Program Files, while the newer one went into 
%USERPROFILE%\AppData\Local\Programs\Python.

This was backed up with all of 5 minutes of experimenting on my own 
computer, on which Windows launches ".py" programs with an old install 
of Python 3.9.9, but the py launcher launches Python 3.12 by default.

Since I am avoiding Windows 11, I can't try anything on it, so my 
thoughts above may not be relevant.

The Python docs for 3.12.1 cover shebang lines at

https://docs.python.org/3/using/windows.html

"If the first line of a script file starts with #!, it is known as a 
“shebang” line. Linux and other Unix like operating systems have native 
support for such lines and they are commonly used on such systems to 
indicate how a script should be executed. This launcher allows the same 
facilities to be used with Python scripts on Windows and the examples 
above demonstrate their use.

To allow shebang lines in Python scripts to be portable between Unix and 
Windows, this launcher supports a number of ‘virtual’ commands to 
specify which interpreter to use. The supported virtual commands are:

/usr/bin/env
/usr/bin/python
/usr/local/bin/python
python

For example, if the first line of your script starts with

#! /usr/bin/python
The default Python will be located and used. As many Python scripts 
written to work on Unix will already have this line, you should find 
these scripts can be used by the launcher without modification. If you 
are writing a new script on Windows which you hope will be useful on 
Unix, you should use one of the shebang lines starting with /usr."

But

"The /usr/bin/env form of shebang line has one further special property. 
Before looking for installed Python interpreters, this form will search 
the executable PATH for a Python executable matching the name provided 
as the first argument. This corresponds to the behaviour of the Unix env 
program, which performs a PATH search. If an executable matching the 
first argument after the env command cannot be found, but the argument 
starts with python, it will be handled as described for the other 
virtual commands. The environment variable PYLAUNCHER_NO_SEARCH_PATH may 
be set (to any value) to skip this search of PATH.

Shebang lines that do not match any of these patterns are looked up in 
the [commands] section of the launcher’s .INI file. This may be used to 
handle certain commands in a way that makes sense for your system. The 
name of the command must be a single argument (no spaces in the shebang 
executable), and the value substituted is the full path to the 
executable (additional arguments specified in the .INI will be quoted as 
part of the filename)."