Using ArcPy and PyGRASS tools in same Python script?

Question

I´m trying to write a Python script, that includes different ArcPy / ArcGIS commands and want to combine it with GRASS geoprocessing tools.

Unfortunately importing the GRASS libraries doesn´t work.

import grass.script as grass

ends in an error:

Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
ImportError: No module named script

I know that GRASS GIS installs it's own Python version. Isn´t there a way to combine the ArcGIS and the GRASS GIS installation of Python? I tried copying the pygrass module (or what I thought it might be it) to the C:\Python26\ArcGIS10.0\Lib\site-packages\ folder. I´m getting a different error message, but it´s still not working.

Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
  File "C:\Python26\ArcGIS10.0\lib\site-packages\grass\script\__init__.py", line 1, in <module>
    from core   import *
  File "C:\Python26\ArcGIS10.0\lib\site-packages\grass\script\core.py", line 38, in <module>
    gettext.install('grasslibs', os.path.join(os.getenv("GISBASE"), 'locale'))
  File "C:\Python26\ArcGIS10.0\lib\ntpath.py", line 96, in join
    assert len(path) > 0
TypeError: object of type 'NoneType' has no len()

I´m using ArcGIS 10 and GRASS 6.4.2 on a Windows 7 64 Bit machine.

Answer 1

Most likely the grass version of Python has installed its own Python bindings into a grass specific site-packages. One non-ideal option would be to add the following prior to importing grass.script:

import sys
sys.path.append('\path\to\grass\bindings.py')

What this is doing is temporarily adding grass to your $PYTHONPATH so that your ArcGIS10.0 Python installation finds it when searching for imports.