QGIS doesnt run from NIX on Ubuntu

[RobBlackwell]

Issue description

I installed Ubuntu 16.04 today as well as NIX. Other packages work
fine, but he NIX installed QGIS fails as follows:

Steps to reproduce

Fresh install of Ubuntu 16.04 and NIX. Install the QGIS package and run it.

Technical details

Warning: loading of qgis translation failed [/nix/store/gfg4gxc29jjy3zgjwbal2fwq045rrrai-qgis-2.18.3/share/qgis/i18n//qgis_en_GB]
Warning: loading of qt translation failed [/nix/store/fx63mg6wsm40zbcs49mlydsxwfhbk9hh-qt-4.8.7/share/qt-4.8.7/translations/qt_en_GB]
Warning: QCss::Parser - Failed to load file  "/style.qss" 
QInotifyFileSystemWatcherEngine::addPaths: inotify_add_watch failed: No such file or directory
Warning: QFileSystemWatcher: failed to add paths: /home/reb/.qgis2//project_templates
Warning: QLayout: Attempting to add QLayout "" to QgsPanelWidgetStack "mWidgetStack", which already has a layout
Traceback (most recent call last):
  File "/nix/store/rbxjyvqs27i41mzb8paj86saiq4ngzxi-python2.7-setuptools-30.2.0/lib/python2.7/site-packages/site.py", line 73, in <module>
    __boot()
  File "/nix/store/rbxjyvqs27i41mzb8paj86saiq4ngzxi-python2.7-setuptools-30.2.0/lib/python2.7/site-packages/site.py", line 34, in __boot
    imp.load_module('site', stream, path, descr)
  File "/usr/lib/python2.7/site.py", line 563, in <module>
    main()
  File "/usr/lib/python2.7/site.py", line 545, in main
    known_paths = addusersitepackages(known_paths)
  File "/usr/lib/python2.7/site.py", line 272, in addusersitepackages
    user_site = getusersitepackages()
  File "/usr/lib/python2.7/site.py", line 247, in getusersitepackages
    user_base = getuserbase() # this will also set USER_BASE
  File "/usr/lib/python2.7/site.py", line 237, in getuserbase
    USER_BASE = get_config_var('userbase')
  File "/usr/lib/python2.7/sysconfig.py", line 582, in get_config_var
    return get_config_vars().get(name)
  File "/usr/lib/python2.7/sysconfig.py", line 528, in get_config_vars
   _init_posix(_CONFIG_VARS)
  File "/usr/lib/python2.7/sysconfig.py", line 412, in _init_posix
    from _sysconfigdata import build_time_vars
  File "/usr/lib/python2.7/_sysconfigdata.py", line 6, in <module>
   from _sysconfigdata_nd import *
ImportError: No module named _sysconfigdata_nd

• System: (NixOS: nixos-version, Ubuntu/Fedora: lsb_release -a, ...)

  $ lsb_release -a
  No LSB modules are available.
  Distributor ID: Ubuntu
  Description: Ubuntu 16.04.1 LTS
  Release: 16.04
  Codename: xenial

• Nix version: (run nix-env --version)

  $ nix-env --version
  nix-env (Nix) 1.11.6

• Nixpkgs version: (run nix-instantiate --eval '<nixpkgs>' -A lib.nixpkgsVersion)

  $ nix-instantiate --eval '' -A lib.nixpkgsVersion
  "17.03pre99424.92b1e39"

[copumpkin]

Looks like it's depending impurely on your system python! 😱

[FRidh]

qgis explicitly asks for the users' site-packages, I guess because it is a feature to install modules as a user. This is something that can always break because we can never guarantee that the users' Python is compatible with ours nor that the users' Python actually works :)

The reason it eventually breaks is because it seems Ubuntu doesn't provide _sysconfigdata_nd where Python looks for it. Note that we actually also don't provide _sysconfigdata_nd (and I have no idea why not).

Furthermore, I saw we still use prefix PYTHONPATH in this expression...

[RobBlackwell]

Thanks - installing the Nix supplied Python2Full package solves the problem.

[FRidh]

installing the Nix supplied Python2Full package solves the problem.

Good to hear the problem is solved. I am surprised that it did solved it though.