Issue while running grass from subprocess

Question

I have a map based web application using geodjango. I needed to display the crime hotspots within a selected polygon area. I found that v.kernel is very good for generating heatmaps/hotspots. So in my application I ran this command through python subprocess and created the raster map showing point density. I displayed this raster map over the polygon area in grass. But when I try to run the command through python using d.out.file command, error is raised.

command5 = "d.mon start=x1" 
command6 = "d.mon select=x1"
command7 = "d.mon unlock=x1"
command8 = "r.colors byr"
command9 = "d.rast crimes_"+str(pname)
command10 = "d.vect "+str(pname)+" type=line,boundary"
command11 = "d.out.file output="+str(pname)+" format=png size=800,600"
command12 = "d.mon stop=x1"

saveCommands = [command4,command5,command6,command7]

for sc in saveCommands:
    s = subprocess.Popen(sc,shell=True,env=environ) 
    s.wait()

Error is :

ERROR: Graph_Set: can't open Display
ERROR: Unable to get GIS_LOCK enviroment variable value
Problem selecting x1. Will try once more
ERROR: Unable to get GIS_LOCK enviroment variable value
d.mon select=x1
Exception AttributeError: AttributeError("'_DummyThread' object has no attribute '_Thread__block'",) in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored
ERROR: Unable to get GIS_LOCK enviroment variable value

All I need is to export the grass vector and raster layer to an image.

Answer 1

Are you sure that you can open a X11 display in a Python process like this. In your case, better use the PNG driver:

d.mon start=PNG
...

See also this manual page: http://grass.osgeo.org/grass64/manuals/pngdriver.html

Answer 2

The error is likely occurring in your command6.

To solve the specific error, you could set the GIS_LOCK environment variable and add it to the environ before it is passed to subprocess.Popen.

environ['GIS_LOCK'] = 'default' # any value should do