Running a Python function in BASH

Question

I usually run Python on Google Colab, however I need to run a script in the terminal in Ubuntu.

I have the following script test.py:

#!/usr/bin/env python

# testing a func

def hello(x):
  if x > 5:
    return "good"
  else:
    return "bad"

hello(2)

When executed it fails to return anything. Now I could just replace the return statements with a print statement. However, for other scripts I have, a return statement is needed.

I tried:

python test.py

You see, on Google Colab, I can simply call the function (hello(2)) and it will execute.

Desired output:

> python test.py
> bad

In Unix (or MacOS or Windows), a child process can't return anything to the parent process (except an exit code, if you count this as return value). Therefore, a program (this includes Python programs) can not return a string. They can print a string to stdout, of course, but you have to tell them to do so. — user1934428
– user1934428, Commented Nov 30, 2022 at 10:52

milanbalazs · Accepted Answer · 2022-11-30 08:27:19Z

2

You don't print anything to STDOUT so you won't see the good/bad in your terminal.

You should change hello(2) line to print(hello(2)) in your code (In this case the return value of hello(2) function call will be printed to STDOUT file descriptor) then you will see your result in your terminal.

answered Nov 30, 2022 at 8:27

milanbalazs

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1 Comment

Marcin Orlowski Over a year ago

Just a note that OP should probably also return proper exit code (be it 0 for "good" and non-zero for "bad")

CamiloSDA · Accepted Answer · 2022-11-30 10:01:15Z

0

In case you want to sent the argument when calling the script you could do it like this:

#!/usr/bin/env python
import sys

def hello(x):
    if x > 5:
        return "good"
    else:
        return "bad"

 print(hello(int(sys.argv[1])))

And so you could call the function like so:

python test.py 6

Then the output would be:

> python test.py 6
> good

edited Nov 30, 2022 at 10:01

answered Nov 30, 2022 at 9:59

CamiloSDA

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