gdal: fix standalone python programs

[vbgl]

This addresses issue #9386.

@michelk: would you like to test? thanks.

[michelk]

Thanks a lot. Just tested locally and this does solve the issue.

[michelk]

I guess QGIS could be fixed in a similar way. Currently, when starting QGIS, I get

Traceback (most recent call last):
  File "/nix/store/8hg8mmi8lb05a673jmv4dfs24hmfrwcs-gdal-2.0.0/lib/python2.7/site-packages/site.py", line 75, in <module>
    __boot()
  File "/nix/store/8hg8mmi8lb05a673jmv4dfs24hmfrwcs-gdal-2.0.0/lib/python2.7/site-packages/site.py", line 35, 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

With the nix-shell-trick, it works.

[vbgl]

@michelk could you be clearer about how you get this QGIS error, please? I cannot reproduce it.

[michelk]

I'm using nixpkgs on a debian system.

With

nix-env -iA nixpkgs.qgis 
qgis

I'm getting the error listed above.

Though

nix-shell -p python qgis
 qgis

works.

[vbgl]

Strange… Are you using any particular plug-in? Is this behaviour new or have you always got such an error?

[domenkozar]

If you fix qgis, I'll also push to release-15.09

[michelk]

I'm using some plug-ins, but when they were failing (eg. missing python-dependency), I got an error and the plugin was automatically disabled, but QGIS was running correctly.

I never used nixpkgs-QGIS in production, since previously there was a mismatch between compiled and running libpng; therefor I always used the debian-QGIS.

[vbgl]

I suggest to merge this PR, as it fixes an issue with gdal. I don’t understand what breaks qgis, so I can’t fix it.