No such file or directory PERMANENT\\MYNAME from Python+Grass?

Question

I have an existing Python script that processes raster images with Gdal / Numpy. Now I want to extend the script with Grass. The python script is developed on Windows 7 with Eclipse/Pydev. The script is executed from within Eclipse. I installed Grass with the OSGeo4W installer (Version 6.4.3). I’m new to Grass, but as far as I understand I first need to create a new GRASS location. I try to do this with:

grass.core.create_location("C:\grassdata", “test”, epsg=21781)

however this throws the following error:

IOError: [Errno 2] No such file or directory:'C:\\grassdata\\test\\PERMANENT\\MYNAME'

create_location first runs g.gisenv, then g.proj and then again g.gisenv and finally tries to open C:\grassdata\test\PERMANENT\MYNAME that does not exists. Actually nothing was created in C:\grassdata. This is the complete script:

import os, sys
import numpy as np
import gdal

def get_env(env):
  value = ""
  if env in os.environ:
    value = os.environ[env] + os.pathsep
  return value

input_data = r"C:\data\dom_eth\DOM_Clip.tif"

# start configure grass
gisbase = os.environ['GISBASE'] = r'C:\OSGeo4W64\apps\grass\grass-6.4.3'

os.environ['GISRC'] = r'C:\Users\Username\AppData\Roaming\GRASS6\grassrc6'
grass_dirs = [os.path.join(os.environ['GISBASE'], i) for i in ['etc', os.path.join('etc', 'python'), 'lib', 'bin', 'scripts']]
path = get_env('PATH') + os.pathsep.join(grass_dirs)
os.environ['PATH'] = path
os.environ['GRASS_SH'] = r'C:\OSGeo4W64\apps\msys\bin\sh.exe'

if not os.path.exists(gisbase):
  os.mkdir(gisbase)

sys.path.append(os.path.join(os.environ['GISBASE'], "etc", "python"))
import grass.script as grass
import grass.script.array as garray
import grass.script.setup as gsetup

gisdbase = r"C:\grassdata"
location = "test"

grass.core.create_location(gisdbase, location, epsg=21781)

A grep -rl "MYNAME" over the source code of Grass did not reveal something useful to me. What is the correct way to use Grass with Python from the "outside"?

Answer 1

you have forgotten an essential part, the initiation of GRASS with setup:

import grass.script as grass
import grass.script.setup as gsetup
gisbase = os.environ['GISBASE']
gisdb="your_path_to/grassdata"
# initiation of GRASS
gsetup.init(gisbase, gisdb)
grass.core.create_location(gisdb,"test", epsg=21781)