[QGIS-Developer] Python27 still main version in Osgeo4W Shell? (QGIS 2.99)

[KOHLMANN Hannes]

Hi folks!

I have a question regarding the Python version in QGIS 3.
I installed the latest nightly build of Qgis 2.99 on Windows 64bit and wanted to start porting self-written QGIS 2 plugins to be QGIS 3 compatible!

My approach would have been to redo the conversion steps with pyuic5 and pyrcc5 (for PyQt5) and then correcting for removed classes.

Now I faced quite exactly the same problem as here:
https://gis.stackexchange.com/questions/260743/how-to-compile-qtdesigner-user-interface-ui-and-resource-qrc-files-with-qg
though, I was not yet successful to get the suggested solution to work, because it is really painful on windows with environment variables. And since I have another independent Python installed, this sometimes becomes a big mess. [Side note: because of that very reason, I will go for NixOS very soon]

So my questions now are:

*) Do you think, that being unable to run pyrcc5.bat properly is caused by the fact that it is searching for Python27 instead of Python36? And as soon as I change the etc\ini\python-core.bat to point to Python36 instead, there seem to be problems with the PATH / PYTHONPATH environment varibles.

*) What is Python27 doing there in first place? Because from my understanding, one major change in QGis3 is to step from 2.7 to 3.6, removing 2.7 completely. Or why is it still there?

The reason of the quite vague formulation of my question might be, that I am not sure, whether the problem caused by me (w.r.t. the environment variables PATH/PYTHONPATH, which is usually the solution to problems with import errors of dlls, modules, etc. under Win) or is it still some early version issue of the Win-Version of QGis 2.99, as Python 2.7 seems still to be there? Or is it a mixture of both? About 15-20 hours of online research have contributed rather to my confusion than to insight :)

If anyone happens to have had similar issues with developing for QGis3 (2.99) on Win + working solutions (e.g. hints regarding the system setup when multiple QGis versions are installed and maybe even another independent Python36 exists), I would really appreciate some help.

Thank you all in advance and best regards,
Hannes
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