Collecting return values from python functions in

Question

I am implementing a bash script that will call a python script's function/method. I want to collect the return valuie of this function into a local variable in the calling bash script.

try1.sh contains:

#!/bin/sh
RETURN_VALUE=`python -c 'import try3; try3.printTry()'`
echo $RETURN_VALUE

Now the python script:

#!/usr/bin/python

def printTry():
    print 'Hello World'
    return 'true'

on excuting the bash script:

$./tr1.sh
Hello World

there is no 'true' or in that place any other type echoed to stdout as is desired.

Another thing I would want to be able to do is, my avtual python code will have around 20-30 functions returning various state values of my software state machine, and I would call these functions from a bash script. In the bash script, I have to store these return values in local variables which are to be used further down the state machine logic implemented in the calling bash script.

For each value, I would have do the python -c 'import python_module; python_module.method_name', which would re-enumerate the defined states of the state machine again and again, which I do not want. I want to avoid making the entire python script run just for calling a single function. Is that possible?

What possible solutions/suggestions/ideas can be thought of here?

I would appreciate the replies.

To clarify my intent, the task is to have a part of the bash script replaced by the python script for improving readability. The bash script is really very large(~ 15000 lines), and hence cannot be replaced by a single python script entirely. So parts which can be idetified to be improved can be replaced by python.

Also, I had thought of replacing the entire bash script by a python script as suggested by Victor in the comment below, but it wouldn't be feasible in my situation. Hence, I would have to have the state machine divided into bash and python, where python would have some required methods returning state values required by the bash script.

Regards, Yusuf Husainy.

Answer 1

If you don't care about what the python function prints to stdout, you could do this:

$ py_ret_val=$(python -c '
from __future__ import print_function
import sys, try3
print(try3.printTry(), file=sys.stderr)
' 2>&1 1>/dev/null)

$ echo $py_ret_val
true