How to use GRASS GIS in Python standalone?

Question

I'm trying to use GRASS module in a Python Skript. I already checked this: Is it possible to use GRASS GIS in Python stand alone scripts? and this Using Python script to control GRASS GIS from outside? but it doesn't help with my problem. I did pip install grass-session which worked well. My script is just: import grass_session and when I run it I get the error RuntimeError: Cannot find GRASS GIS start script: 'grass', set the right one using the GRASSBIN environm. variable.

First I tried GRASSBIN="$path\\to\\software\\grass\\grass78 python grass.py" as suggested in https://grasswiki.osgeo.org/wiki/Working_with_GRASS_without_starting_it_explicitly in the block Python: GRASS GIS 7 with an external library: grass-session but I still got the same error.

After checking http://osgeo-org.1560.x6.nabble.com/GRASSBIN-environment-variable-td5413301.html I solved this error adding the following line before the import line: os.environ['GRASSBIN']=r"path\to\software\grass\grass78", although I feel this only should be necessary if my grass version is different from 7.8.

Now when I run these two lines first I'm happy to see that I don't get the error again but after a while I notice that nothing happens. It keeps running without any exit code unless I stop the script manually. I would expect the script to import the module and finish with exit code 0.

I have grass gis 7.8.2. installed with QGIS and Python 3.7 and working on Windows 10 Pro 64 bit.

Answer 1

If you have already started GRASS interactively, and created a LOCATION/MAPSET, then try the full code example:from the wiki.

If you do not yet have your GRASS DB setup, and you want to try constructing a temporary location using python, then the next wiki section gives a working example.

Please try those complete examples, then post back if something does not work.

Edited:

You should not have to do any pip install grass. In the setup script are the lines:

# Set GISBASE environment variable
os.environ['GISBASE'] = gisbase
# define GRASS-Python environment
gpydir = os.path.join(gisbase, "etc", "python")
sys.path.append(gpydir)

If you have GRASS installed, that should take care of finding the GRASS python module grass.script. Can you double check that you are getting the paths correct, etc.??

• anplaceb: Hi Micha, sorry for the delay, I had holiday. I've tried the second option because it works better for me but I noticed that the code is written in python 2 and I had to addapt some parts to python 3. Now the code was able to create a new location but I get the error: import grass.script as grass ModuleNotFoundError: No module named 'grass.script'; 'grass' is not a package
• anplaceb: After doing pip install grass, setting the grassbin env manually with os.environ['GRASSBIN'] = r"path" and importing grass_session before the import grass.script as grass line, it trhrows the next error at line grass.message('--- GRASS GIS 7: Current GRASS GIS 7 environment:') The error is very long and I can only copy the last part: grass.exceptions.CalledModuleError: Module run None g.gisenv -n ended with error Process ended with non-zero return code 3221225781. See errors in the (error) output.
• Micha: If you have GRASS installed, you should not do pip install grass. See edits above.
• anplaceb: I think my paths are corerct gisbase: D:\path\to\QGIS_3.10\apps\grass\grass78 gpydir: D:\path\to\QGIS_3.10\apps\grass\grass78\etc\python with these paths I get the error no module named 'grass.script'; 'grass' is not a package
• anplaceb: I get the other error grass.exceptions.CalledModuleError: Module run None g.gisenv -n ended with error Process ended with non-zero return code 3221225781. See errors in the (error) output. by changing 'etc' to 'Python' in the gpydir path, which I did just for trying and I was surprised to see that that way I avoid the import error, but to be honest I'm not sure why

Answer 2

Edited 6/2024 (dropping "grass-session"):

Starting with GRASS GIS version 8.4+, the "grass-session" pip package is no longer needed, but an internal Python API is now provided.

This example performs a small statistical calculation on a LAZ file (simple.laz) with [r.in.pdal][3].

First set the Python path and start Python:

export PYTHONPATH=$(grass --config python-path)
python

Next we import the GRASS GIS Python bindings and test r.in.pdal:

import grass.script as gs
import urllib.request
# download a small sample data file (LiDAR points)
urllib.request.urlretrieve(
 "https://github.com/OSGeo/grass/raw/main/docker/testdata/simple.laz",
 "/tmp/simple.laz",
)
# full path to new project
project = "/tmp/grassproject_epsg_25832"
gs.create_project(project, epsg="25832")
# initialize project (formerly: location)
gs.setup.init(project)
print("GRASS GIS session: tests for PROJ, GDAL, PDAL, GRASS GIS")
print(gs.parse_command("g.gisenv", flags="s"))
# simple test: scan the LAZ file for boundary extent
gs.run_command(
 "r.in.pdal",
 input="/tmp/simple.laz",
 output="count_1",
 method="n",
 flags="g",
 resolution=1,
 overwrite=True,
)

• Francesco Frassinelli: It looks nice, but it is not maintained.
• markusN: Good point. I have edited it, dropping the need for "grass-session" pip package.
• unbutu: is there a solution that is an simple as pip install ___<whatever is needed to get grass to work as stand alone python library>_____? where do I installl grass.script from?