subprocess cannot run python executable in non-interactive mode?

Question

I am using python 3.6.3 and subprocess module to run another python script

#  main.py

#!/bin/env python
from subprocess import Popen,PIPE
from sys import executable

p = Popen([executable, 'test.py', 'arg1'],shell=True, stdout=PIPE)
p.wait()
print(p.stdout.read().decode())

and

#  test.py

import sys
print(sys.argv)

I expect it will run and execute test.py. However, it opens an python interpreter in interactive mode!

I tested shell=False option, it works. I tested string form rather than list form of args, it works.

I am not sure if it is a bug or not.

CPython will drop to interactive mode if it's stdin is connected to a TTY. The default of Popen is for the default io handles to be inherited, which connects the second interpreter to your TTY as well. Try passing stdin=None. — user2722968
– user2722968, Commented May 17, 2018 at 18:14
@user2722968 I'm unable to see that behavior with Python 3.6.5rc1. If I run python3 test.py arg1 from my terminal (where stdin is a tty), it runs the script without dropping to an interactive shell. — that other guy
– that other guy, Commented May 17, 2018 at 18:27

khachik · Accepted Answer · 2018-05-17 18:13:41Z

2

You need to remove shell=True or change the first argument to be executable + ' test.py arg1' instead of [executable, 'test.py', 'arg1'].

As explained in the documentation, with shell = True, it will run it as /bin/sh -c python test.py arg1, which means python will be run without arguments.

edited May 17, 2018 at 18:13

answered May 17, 2018 at 18:10

khachik

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2 Comments

user2722968 Over a year ago

This is horrible and will lead to problems with more complex arguments

khachik Over a year ago

It is reasonable, the docs explain how it works. What can really lead to problems is using something without understanding how it works.

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