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I have gone through the following steps:

  1. Installed the following packages that came with QGIS 2.18:
    1. 1 GDAL Complete.pkg
    2. 2 NumPy.pkg
    3. 3 matplotlib.pkg
    4. 4 Install QGIS.pkg
  2. Installed GRASS-7.4.1 from GRASS GIS for Mac by drag-and-droping it into the /Applications folder.

When I now try to run v.net.nodes in the processing toolbox, I get the following errors:

unsupported operand type(s) for +: 'NoneType' and 'str' See log for more details

It seems that GRASS GIS 7 is not correctly installed and configured in your system. Please install it before running GRASS GIS 7 algorithms.

The log reads the following:

2   Uncaught error while executing algorithm
Traceback (most recent call last):
File "/Applications/QGIS.app/Contents/MacOS/../Resources/python/plugins/processing/core/GeoAlgorithm.py", line 203, in execute
self.processAlgorithm(progress)
File "/Applications/QGIS.app/Contents/MacOS/../Resources/python/plugins/processing/algs/grass7/Grass7Algorithm.py", line 297, in processAlgorithm
Grass7Utils.executeGrass7(self.commands, progress, self.outputCommands)
File "/Applications/QGIS.app/Contents/MacOS/../Resources/python/plugins/processing/algs/grass7/Grass7Utils.py", line 298, in executeGrass7
command, grassenv = Grass7Utils.prepareGrass7Execution(commands)
File "/Applications/QGIS.app/Contents/MacOS/../Resources/python/plugins/processing/algs/grass7/Grass7Utils.py", line 289, in prepareGrass7Execution
command = Grass7Utils.command + ' ' + os.path.join(Grass7Utils.grassMapsetFolder(), 'PERMANENT')
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'
1   There were errors executing the algorithm.

I am guessing that Grass7Utils.command is Null, which tells me, that Grass7Utils.py does not know where to search for GRASS 7.

Do I need to configure QGIS for it to know where to find GRASS 7? If yes, how is this done?

  • Does this error arise when calling any GRASS module or just v.net.nodes (or a few modules)? – markusN Dec 9 '18 at 18:11

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