Python pass a variable to another script

Question

I am new to python so my apologies in advance if the question is somewhat dumb or unrealistic.

I have an internally developed tool that converts traces of an ECU to a human readable data with the help of some self-developed python packages that I don’t have access to.

I want to “export” some signal values obtained in this tool (that I can store in a python list in the tool) to an external python script where I can do some additional processing. Something like this: inTool.py

#do some trace processing, get signal_values as a result 
def when_done():
   start external python script and give it signal_values as input

external_Script.py

#import signal_values from inTool.py and do some additional processing.

Is this doable?

Reason: the tool cannot handle third-party packages well and often crashes. That is why solutions similar to this don’t work for me .

My last resort would probably be to write the values to a text file in the tool and read them out again in my script but I was wondering if there is a nicer way to do it. Thanks!

tdelaney · Accepted Answer · 2020-12-14 22:15:53Z

3

Writing to an intermediate file is fine, lots of tools do it. You could write your script to use a file or read from its sys.stdin. Then you have more options on how to use it.

external_script.py

import sys

def process_this(fileobj):
    for line in fileobj:
        print('process', line.strip())

if __name__ == "__main__":
    # you could use `optparse` to make source configurable but
    # doing a canned implementation here
    if len(sys.argv) == 2:
        fp = open(sys.argv[1])
    else:
        fp = sys.stdin
    process_this(fp)

The program could write a file or pipe the data to the script.

import subprocess as subp
import sys

signal_values = ["a", "b", "c"]
proc = subp.Popen([sys.executable, "input.py"], stdin=subp.PIPE)
proc.stdin.write("\n".join(signal_values).encode("utf-8"))
proc.stdin.close()
proc.wait()

You could pipeline through the shell

myscript.py | external_script.py

edited Dec 14, 2020 at 22:15

answered Dec 14, 2020 at 21:35

tdelaney

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2 Comments

bald_cactus Over a year ago

Thanks for showing the way! My signal_values is a dictionary {signal_name : values} and I only get the keys when I try your method. Am I missing something or how do I also get the values?

tdelaney Over a year ago

Data needs to be serialized to move between processes and there are lots of options. You could use JSON, convert to a CSV, use a python pickle or a hundred other options.

quamrana · Accepted Answer · 2020-12-14 21:25:26Z

3

The usual way of passing data from one script to another is to just import the destination function and call it:

# inTool.py
from external_script import additional

def when_done():
    signal_values = ...        # list referenced by signal_values
    additional(signal_values)  # directly call function in external_script.py

answered Dec 14, 2020 at 21:25

quamrana

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Comments

Jessie Wilson · Accepted Answer · 2022-04-13 21:42:19Z

0

I know this is an older post. I searched for a while for a solid answer and quamrana's response was the best. I'm going to just add to it a little to show a working example.

main.py from other_script import run_this_test

def do_something():
    var = "Hello World!"
    run_this_test(var)

do_something()

other_script.py

def run_this_test(x):
print(x)

This is my first time posting something like this on here, I know it's basic, but this worked for me!

answered Apr 13, 2022 at 21:42

Jessie Wilson

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