Is it possible to cross reference bash and python variables in python script

Question

I can get a value n when I run a shell command using os.system in the python script, but I also need to sum it up to get a total number for subsequent computation in the python script,

total=0
for i in xrange(1,8):
    os.system('n=$(qstat -n1 | grep -o node'+str(i)+' | wc -l)  && echo $n')

Is it possible? Also is it possible to use python variable in shell command, something like

os.system('echo $total')

Answer 1

Use the shell's export command:

$ export ABC=1 # Set and export var in shell 
$ bash # Start another shell
$ echo $ABC # variable is still here
1
$ python # Start python still in the deeper shell
Python 2.7.2 (default, Oct 11 2012, 20:14:37)
[GCC 4.2.1 Compatible Apple Clang 4.0 (tags/Apple/clang-418.0.60)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from os import environ # import environnement
>>> environ['ABC'] # And here's the variable again (it's a string because the shell doesn't have types)
'1'

Answer 2

You can subprocess module's check_output method like this

import subprocess
print sum(int(subprocess.check_output(["/bin/sh", "-c", "n=`expr {} + 1` && echo $n".format(i)])) for i in range(10))

Output

55