GRASS GIS – Getting GRASS 7.4.4 Working in Python 3

grassgrass-7.4pythonpython 3

I'm trying to get some GRASS functionality in a Python Script, specification r.series, but I'm struggling to import GRASS. I'm trying to uses the method outline on the GRASS Wiki, Working with GRASS without starting it explicitly, by using this code script.setup module but with these modification:

import os
import sys
import subprocess

# define GRASS Database
gisdb = "D:\GRASS_DB"

# specify (existing) Location and Mapset
location = "LearnGRASS"
mapset = "PERMANENT"

# path to the GRASS GIS launch script
grass7bin = r'C:\Program Files\GRASS GIS 7.4.4\grass74.bat'

# query GRASS GIS itself for its GISBASE
startcmd = [grass7bin, '--config', 'path']
try:
    p = subprocess.Popen(startcmd, shell=False,
                     stdout=subprocess.PIPE, stderr=subprocess.PIPE)
out, err = p.communicate()
except OSError as error:
    sys.exit("ERROR: Cannot find GRASS GIS start script"
         " {cmd}: {error}".format(cmd=startcmd[0], error=error))
if p.returncode != 0:
    sys.exit("ERROR: Issues running GRASS GIS start script"
         " {cmd}: {error}".format(cmd=' '.join(startcmd), error=err))
gisbase = out.strip(os.linesep)

# set GISBASE environment variable
os.environ['GISBASE'] = gisbase

# define GRASS-Python environment
grass_pydir = os.path.join(gisbase, "etc", "python")
sys.path.append(grass_pydir)

# import (some) GRASS Python bindings
import grass.script as gscript
import grass.script.setup as gsetup

# launch session
rcfile = gsetup.init(gisbase, gisdb, location, mapset)

# example calls
gscript.message('Current GRASS GIS 7 environment:')
print(gscript.gisenv())

gscript.message('Available raster maps:')
for rast in gscript.list_strings(type='raster'):
    print(rast)

gscript.message('Available vector maps:')
for vect in gscript.list_strings(type='vector'):
    print(vect)

# delete the rcfile
os.remove(rcfile)

However, I am getting this error message:

Traceback (most recent call last):
File "D:/Training/LearnGRASS/LearnGRASS_7.py", line 28, in
gisbase = out.strip(os.linesep)
TypeError: a bytes-like object is required, not 'str'

It apppead that the offend line was this one:

gisbase = out.strip(os.linesep)

where the script is trying to remove the endline characters from out, so I modified the line to:

gisbaseStr = str(out).replace("\\n'", "").replace("b'", "")
gisbase = str.encode(gisbaseStr)

However, that return the error message:

Traceback (most recent call last):
File "D:/Training/LearnGRASS/LearnGRASS_7.py", line 34, in
os.environ['GISBASE'] = gisbase
File "C:\Users\bradl\Anaconda2\envs\GeoSpatial_3.6\lib\os.py", line 674, in setitem
value = self.encodevalue(value)
File "C:\Users\bradl\Anaconda2\envs\GeoSpatial_3.6\lib\os.py", line 730, in check_str
raise TypeError("str expected, not %s" % type(value).name)
TypeError: str expected, not bytes

But leaving it as a string kick up different Error Message:

Traceback (most recent call last): File "C:\Program Files\GRASS GIS 7.4.4\etc\python\grass\script\core.py", line 39, in
import builtin ModuleNotFoundError: No module named 'builtin'

During handling of the above exception, another exception occurred:

Traceback (most recent call last): File
"D:/Training/LearnGRASS/LearnGRASS_7.py", line 41, in
import grass.script as gscript File "C:\Program Files\GRASS GIS 7.4.4\etc\python\grass\script__init__.py", line 5, in
from .core import * File "C:\Program Files\GRASS GIS 7.4.4\etc\python\grass\script\core.py", line 44, in
from os import environb as environ ImportError: cannot import name 'environb'

Best Answer

Please switch to GRASS GIS 7.7 if you need Python3 support. A lot of effort has already been invested here (which will not be backported to older versions).

You will save plenty of time (and not reinvent the wheel) when switching to GRASS GIS 7.7+. Details are found at https://trac.osgeo.org/grass/wiki/Python3Support

Edit: Since yesterday there are ready-to-use WinGRASS7.7 binaries available, see here (and here).

Edit Sep 2019:

GRASS GIS 7.8.0 with Python 3 support as been released:

https://trac.osgeo.org/grass/wiki/Release/7.8.0-News

Related Solutions

GRASS GIS – Connecting Python Script External to GRASS GIS 7 Program in Windows 10

The linked says you need to set environmental variables. This is done in Python using e.g.:

import os
os.environ['GISBASE'] = "/some/path"

The syntax

PYTHONPATH = 'C:\OSGeo4W\apps\grass\grass-7.0.4\etc\python'

in Python just sets a variable (global one in your case) which is just a Python variable, nothing more, nothing less. The aforementioned wiki just lists the environmental variables to be set. How you set them is up to you. You can do it ahead in the command line before starting Python, you can change it in the system (search the Internet for how to do it in some GUI for your version of MS Windows), or you can use Python (os.environ).

Here is an example how to setup the environment (simplified from GRASS Python doc):

import os
import sys
import subprocess

grass7bin = r'C:\Program Files\GRASS GIS 7.0.4\grass70.bat'
startcmd = [grass7bin, '--config', 'path']
try:
    p = subprocess.Popen(startcmd, shell=False,
                         stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    out, err = p.communicate()
except OSError as error:
    sys.exit("ERROR: Cannot find GRASS GIS start script"
             " {cmd}: {error}".format(cmd=startcmd[0], error=error))
if p.returncode != 0:
    sys.exit("ERROR: Issues running GRASS GIS start script"
             " {cmd}: {error}"
             .format(cmd=' '.join(startcmd), error=err))
gisbase = out.strip(os.linesep)

os.environ['GISBASE'] = gisbase
grass_pydir = os.path.join(gisbase, "etc", "python")
sys.path.append(grass_pydir)

import grass.script.setup as gsetup

gisdb = os.path.join(os.path.expanduser("~"), "Documents/grassdata")
location = "nc_spm_08"
mapset = "user1"

rcfile = gsetup.init(gisbase, gisdb, location, mapset)

# use grass functions here

os.remove(rcfile)

Now you put your GRASS module calls and GRASS Python API function calls to the place where # use grass functions here is.

Note that you don't do anything from the above if you just run the code from inside GRASS GIS session. However, the code once you have the environment done in the right way is the same and looks for example like this:

import grass.script as gscript

gscript.run_command('g.region', s=10, n=50, w=30, e=60, res=2)
gscript.mapcalc('test1 = sin(col() + row())')
print gscript.read_command('r.info', map='test1', flags='g')
print gscript.parse_command('r.univar', map='test1', flags='g')

[GIS] How to use GRASS GIS in Python standalone

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.??

Best Answer

Related Solutions

GRASS GIS – Connecting Python Script External to GRASS GIS 7 Program in Windows 10

[GIS] How to use GRASS GIS in Python standalone

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