PyGRASS error: Could not load grass_gis.8.2

Question

In PyGRASS I can only import objects from the module modules:

from grass_session import Session
from grass.pygrass.modules import Module, MultiModule, ParallelModuleQueue

print(Module)

If I'm trying to import other PyGRASS modules like vector I am getting an error:

from grass_session import Session
from grass.pygrass.vector import VectorTopo

Traceback (most recent call last):
  File "/Users/jonas.frei/Documents/Python/pygrass01/main.py", line 2, in <module>
    from grass.pygrass.vector import VectorTopo
  File "/Applications/GRASS-8.2.app/Contents/Resources/etc/python/grass/pygrass/vector/__init__.py", line 4, in <module>
    import grass.lib.gis as libgis
  File "/Applications/GRASS-8.2.app/Contents/Resources/etc/python/grass/lib/gis.py", line 30, in <module>
    _libs["grass_gis.8.2"] = load_library("grass_gis.8.2")
  File "/Applications/GRASS-8.2.app/Contents/Resources/etc/python/grass/lib/ctypes_loader.py", line 105, in __call__
    raise ImportError("Could not load %s." % libname)
ImportError: Could not load grass_gis.8.2.

I already tried to fix this error in so many ways:

• MacOS, GRASS GIS 8.2, grass_session
• MacOS, GRASS GIS 8.2, 'Python: GRASS GIS 7 without existing location using metadata only'-script
• Windows, GRASS GIS 8.2, grass_session
• Windows, GRASS GIS 7.8, grass_session

I'm using the following environment variables:

• MacOS
  • GRASSBIN=/Applications/GRASS-8.2.app/Contents/Resources/bin/grass
  • LD_LIBRARY_PATH=/Applications/GRASS-8.2.app/Contents/Resources/lib
  • GISBASE=/Applications/GRASS-8.2.app/Contents/Resources
  • PATH="$PATH:/Applications/GRASS-8.2.app/Contents/Resources/bin"
• Windows
  • PATH=%PATH%;C:\OSGeo4W\bin
  • GRASSBIN=C:\OSGeo4W\bin\grass78
  • LD_LIBRARY_PATH=C:\OSGeo4W\apps\grass\grass78\lib
  • GISBASE=C:\OSGeo4W\apps\grass\grass78

Answer 1

Hint: Let me recommend to use GRASS GIS 8 (and no longer 7.8).

So, in a running GRASS GIS 8 session, run in python:

import os
import subprocess
import sys

# define GRASS data settings (adapt to your needs)
grassdata = "/home/mneteler/grassdata/"
location = "nc_spm_08_grass7"
mapset = "user1"

# Python path: we ask GRASS GIS where its Python packages are
sys.path.append(
    subprocess.check_output(["grass", "--config", "python_path"], text=True).strip()
)

# Import GRASS Python bindings
import grass.script as gs
import grass.script.setup as gsetup

# Start GRASS Session
session = gsetup.init(grassdata, location, mapset)

At this point we are in a running GRASS GIS session, let's verify.

# show current GRASS GIS settings
print(gs.read_command("g.gisenv"))

Now we may also import further functionality (e.g. VectorTopo of pygrass):

from grass.pygrass.vector import VectorTopo

and can for example retrieve the topology of a vector map (using the North Carolina dataset):

test_vect = VectorTopo("zipcodes_wake")
test_vect.open(mode="r")
test_vect.num_primitive_of("point")
test_vect.num_primitive_of("line")
test_vect.num_primitive_of("centroid")
test_vect.num_primitive_of("boundary")
test_vect.close()

This should report:

>>> test_vect.num_primitive_of('point')
0
>>> test_vect.num_primitive_of('line')
0
>>> test_vect.num_primitive_of('centroid')
48
>>> test_vect.num_primitive_of('boundary')
158

Answer 2

You can add the missing GRASS GIS libraries into your LD_LIBRARY_PATH (or on OSX it will be: DYLD_LIBRARY_PATH)

You can add it on top of your script:

import os

os.environ['LD_LIBRARY_PATH'] = '/usr/lib/grass82/lib/'

Then MarkusN example will also work in a standalone script or in a jupyter notebook. see example (assumes grass-session is installed)