Fix automatic package installation when using conda forge qgis

[m-richards]

I've been experimenting with using QGIS installed via conda-forge (same idea as this) as a way to keep qgis up to date more easily, and I noticed that the automatic pip install as part of the plugin download is broken when qgis is packaged in this way.

This was the traceback I got

Traceback (most recent call last):
  File "C:\Users/Matt/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\qaequilibrae\qaequilibrae.py", line 33, in 
    from aequilibrae.project import Project
  File "C:\Users/Matt/.conda/envs/qgis/Library/./python\qgis\utils.py", line 888, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
ModuleNotFoundError: No module named 'aequilibrae'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users/Matt/.conda/envs/qgis/Library/./python\qgis\utils.py", line 423, in _startPlugin
    plugins[packageName] = package.classFactory(iface)
  File "C:\Users/Matt/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\qaequilibrae\__init__.py", line 3, in classFactory
    from .qaequilibrae import AequilibraEMenu
  File "C:\Users/Matt/.conda/envs/qgis/Library/./python\qgis\utils.py", line 888, in _import
    mod = _builtin_import(name, globals, locals, fromlist, level)
  File "C:\Users/Matt/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\qaequilibrae\qaequilibrae.py", line 43, in 
    result = download_all().install()
  File "C:\Users/Matt/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\qaequilibrae\download_extra_packages_class.py", line 25, in install
    command = f'"{self.find_python()}" -m pip install -r "{self.file}" -t "{self.pth}" --upgrade'
  File "C:\Users/Matt/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\qaequilibrae\download_extra_packages_class.py", line 64, in find_python
    raise FileExistsError("Can't find a python executable to use")
FileExistsError: Can't find a python executable to use

and it seemed pretty straightforward to just add another condition to the windows path lookup.

As an aside, if the default was to use plain python python, rather than crash with a FileExistsError (or at least attempt to do so), as it looks like the behaviour was before #213 this would have worked without issue for me (based on testing, that, I wasn't able to install and old commit directly to check).

If this is considered out of scope that's fine too, I don't know if the assumption that qgis is bundled with a specific version of python is made, but installing from conda forge would break that - as you can specify qgis and python versions explicitly.

(I also added some things to the gitignore that showed, but that might be a side effect of how I did my dev setup)

[pedrocamargo]

@m-richards , nice to see you around here!! QGIS does ship with a specific version of Python on Windows, so that is definitely necessary for the average user

[m-richards]

@m-richards , nice to see you around here!! QGIS does ship with a specific version of Python on Windows, so that is definitely necessary for the average user

Nice to finally have a small excuse to to play with some of aequilibrae.

Yep, I'm aware that's the usual situation but I don't know if violating that assumption would break the plugin. I see aequilibrae has wheels per platform and python minor release, so as long as the right python is detected, there shouldn't be any issues? I suppose the conda case could be further boxed off by checking for "conda" in sys.version but this seems flakey.

I notice the CI is having some trouble, It looks like one is not looking for a branch on a fork, and the other is looking for secrets which I guess also wouldn't be on a fork.

[jamiecook]

Hey @m-richards - sorry for delay in reviewing - i just tested out your suggestion to use sys.base_prefix and can confirm it works nicely for a stock windows install. If it also works for conda i think we'd take a punt that it's going to work for OSGEO installations too.