[QGIS-Developer] Python regression in the latest patch release 3.34.3

[Johannes Kröger (WhereGroup)]

Hi Lauri,

have you considered using the python-qgis.bat/python-qgis-ltr.bat 
instead? That should set all PATHs etc correctly.

Cheers, Hannes

On 31.01.24 08:57, Lauri Kajan via QGIS-Developer wrote:
> Hi all,
>
> This might be more of an OSGeo4W issue, but I wanted to bring it to 
> your attention.
>
> Unfortunately, something has changed in the latest patch release 
> 3.34.3 on Windows regarding Python.
> The logic of how Python finds its DLLs has changed somehow. I know 
> that Python has upgraded to 3.9.18 to get necessary security updates.
>
> We have relied on the process where we create a virtual environment 
> for plugin development. We have previously created it with command
> `C:\Program Files\QGIS 3.34.3\apps\Python39\python.exe -m venv 
> --system-site-packages .venv`
> We have then set the needed module lookup path with a `pth`-file and 
> dll paths with the `sitecustomize.py` in the virtual environment.
>
> This has worked great previously but now fails.
> The first error I got is that `zlib.dll` was not found. This can be 
> “fixed” by copying it to `C:\Program Files\QGIS 3.34.3\apps\Python39` 
> (which I would prefer not to do since our training clients don’t 
> necessarily have permissions for that on their computers).
> The second problem comes when `pip` is tried to be installed to the 
> venv by `ensurepip`. This step fails because python.exe won’t find its 
> `python39.dll`.
> The venv can be created with `--without-pip` flag but after activating 
> the vevn and calling python.exe, it also fails to start and gives an 
> error `python39.dll` is not found. How come python.exe can't find the 
> DLL file from `apps\Python39` which is correctly set as `home` in the 
> `pyvenv.cfg`?
> If the `C:\Program Files\QGIS 3.34.3\apps\Python39` folder is added to 
> `PATH`, then python39.dll can be found. This is also a step I would 
> prefer not to be necessary.
>
>
> Is this something that was expected in the Python upgrade?
> Has this changed in Python itself or has something changed in OSGeo4W 
> packaging?
> Is it expected that the previous mode of operation will be restored?
>
> Does anyone have any ideas on how to overcome this?
>
>
> Regards,
>
> Lauri
>
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-- 
Johannes Kröger / GIS-Entwickler/-Berater

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