Setting Up Windows System Variables with Python - operating-system

Question

I am looking to set up two separate system variables through python, so that both gdal_calc and gdal_translate will work properly on my computer. However, it the pathway's that I have appended and the variables that I have added don't seem to be working properly. Any suggestions?
#!/usr/bin/env python
import subprocess
from subprocess import call
import sys
import os
# make dictionary of environmental variables to set up for gdal_calc and gdal_translate
gdal_env = os.environ.copy()
# modify and add variables for environment so that GDAL runs properly
gdal_env["GDAL_DATA"] = "C:\\Program Files (x86)\\GDAL\\gdal-data"
gdal_env["GDAL_DRIVER_PATH"] = "C:\\Program Files (x86)\\GDAL\\gdalplugins"
gdal_env["PATH"] = gdal_env["PATH"] + ";C:\\Program Files (x86)\\GDAL\\bin"
# Set constants
# The pathway to the images files are nested within the '--outfile=' command
inHVFile = os.path.expanduser('~\\Desktop\\Components\\Float32\\newHV32.img')
outPlacement = os.path.expanduser('~\\Desktop\\Components\\Zeros\\newHVZeros_1.img')
outVFile = '--outfile=' + outPlacement
#calc_cmd_HV = ['gdal_calc.py', '-A', inHVFile, outVFile, '--calc=A+1']
inVHFile = os.path.expanduser('~\\Desktop\\Components\\Float32\\newVH32.img')
outPlacement_1 = os.path.expanduser('~\\Desktop\\Components\\Zeros\\newVHZeros_1.img')
outVFile_1 = '--outfile=' + outPlacement_1
#calc_cmd_VH = ['gdal_calc.py', '-A', inVHFile, outVFile_1, '--calc=A+1']
subprocess.call([sys.executable,'C:\Program Files (x86)\GDAL\gdal_calc.py', inHVFile, outVFile, '--calc=A+1'], env=gdal_env)
subprocess.call([sys.executable,'C:\Program Files (x86)\GDAL\gdal_calc.py', inVHFile, outVFile_1, '--calc=A+1'], env=gdal_env)
#subprocess.call([sys.executable, 'C:\\Program Files (x86)\\GDAL\\gdal_calc.py','-A', inHVFile, outVFile, '--calc=A+1'])
#subprocess.call([sys.executable, 'C:\\Program Files (x86)\\GDAL\\gdal_calc.py','-A', inVHFile, outVFile_1, '--calc=A+1'])

Answer 1

Environmental variables hold information about where files and programs can be found. When using Python to call commandline programs via subprocess.call or subprocess.Popen, you can specify a set of environmental variables at the time the subprocess is spawned. This is done by passing a dictionary to the env kwarg of call or Popen. If env is not specified, the default environmental variables will be used.
Modifications to the environmental variables stored in os.environ will not persist after the Python session has ended.
To call GDAL programs via subprocess.call, do the following:
import os
import subprocess
import sys
# make dictionary of environmental variables
gdal_env = os.environ.copy()
# modify and add variables
gdal_env["GDAL_DATA"] = "C:\\Program Files (x86)\\GDAL\gdal-data"
gdal_env["GDAL_DRIVER_PATH"] = "C:\\Program Files (x86)\\GDAL\\gdalplugins"
gdal_env["PATH"] = gdal_env["PATH"] + ";C:\\Program Files (x86)\\GDAL\\bin"
# ... do preparation ...
a = "a.tif"
b = "b.tif"
output = "output.tif"
calc_cmd = [sys.executable, 'gdal_calc.py', '-A', a, '-B', b, '--outfile='+output, '--calc=A+B']
# spawn a new subprocess
subprocess.call(calc_cmd, env=gdal_env)