Help getting operator input to python shell script running from Automator

Here is how you run python3 from Apple's Command Line tools in an Automator Run Shell Script. You sys.argv[1:] items are passed into the script via the "${@}" indicator on the python3 invocation line.

 /usr/bin/python3 <<'EOF' - "${@}"

import subprocess
import sys
import os

try:
    from subprocess import DEVNULL   # python3
except ImportError:
    DEVNULL = open(os.devnull, 'wb') # python2

ascript = '''
use scripting additions

set userCanceled to false
set school_software to {"PowerSchool", "Infinite Campus", "ReName Only"}
set this_prompt to "Select one choice for School software"

try
    set choice to (choose from list school_software¬
    with title "School Software Selection"¬
    with prompt this_prompt¬
    default items (item 1 of school_software)¬
    OK button name "Select")
on error number -128
    set userCanceled to true
end try
if not userCanceled then
    return (choice as text)
else
    return 0
end if
'''

def main():

    try:
        proc = subprocess.check_output(['osascript', '-e', ascript],
                                       shell=False, stderr=DEVNULL)

        if 'Cancel' in proc.decode('utf-8'):  # User pressed Cancel button
            raise subprocess.CalledProcessError
    except subprocess.CalledProcessError as e:
        print('Python error: [%d]\n%s\n'.format(e.returncode, e.output))
        sys.exit(e.output)
    # show valid response
    print(proc.decode('utf-8').strip())


if __name__ == '__main__':
    sys.exit(main())

EOF