Subprocess stdin input

Question

I'm trying to pass arguments to my test_script.py but I'm getting the following error. I know this isn't the best way to do this but it's the only one that will work since I won't know what functions are in test_script.py. How can I pass arguments as stdin input?

test_script.py

a = int(input())
b = int(input())

print(a+b)

main_script.py

try:
  subprocess.check_output(['python', 'test_script.py', "2", "3"], stderr=subprocess.STDOUT)
except subprocess.CalledProcessError as e:
  print(e.output)

Error

b'Traceback (most recent call last):\r\n File "test_script.py", line 1, in <module>\r\n a = int(input())\r\nEOFError: EOF when reading a line\r\n'

in `main_script` you are passing numbers as argument but in `test_script` you are trying to read them from `stdin` — Saeid, Nov 28 '15 at 20:34
A script that test other scripts, you type input data and read the output, an if you know correct output you can see if the script is working properly — Nobbie, Nov 28 '15 at 21:10
If it did not help then you must not have read the it because it does exactly what you want — Padraic Cunningham, Nov 29 '15 at 01:52
***(1)*** put the code from `test_script.py` into a function (the function is `func = lambda a, b: a + b` in this case) then import the module and call the function: `import the_module; print(the_module.func(2, 3))` (assuming `test_script.py` is renamed to `the_module.py`) -- [related question](http://stackoverflow.com/q/30076185/4279). OR ***(2)*** if you want to pass input to a subprocess (doesn't matter how it is implemented) via its stdin then see [Python - How do I pass a string into subprocess.Popen (using the stdin argument)?](http://stackoverflow.com/q/163542/4279) — jfs, Nov 29 '15 at 08:52

score 1 · Accepted Answer · edited May 23 '17 at 12:23

1

If do not want to use argv, however is odd, consider Popen and operating/communicating on stdin/stdout

from subprocess import Popen, PIPE, STDOUT

p = Popen(['python', 'test_script.py'], stdout=PIPE, stdin=PIPE, stderr=STDOUT)

p_stdout = p.communicate(input=b'1\n2\n')[0]
# python 2
# p_stdout = p.communicate(input='1\n2\n')[0]
print(p_stdout.decode('utf-8').strip())
# python2
# print(p_stdout)

As a reference from SO Python subprocess and user interaction.

And even more info on https://pymotw.com/2/subprocess/

edited May 23 '17 at 12:23

Community

1
1

answered Nov 28 '15 at 21:13

kwarunek

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I'm getting error: `p_stdout = p.communicate(input='1\n2\n')[0] File "C:\Python34\lib\subprocess.py", line 959, in communicate stdout, stderr = self._communicate(input, endtime, timeout) File "C:\Python34\lib\subprocess.py", line 1195, in _communicate self.stdin.write(input) TypeError: 'str' does not support the buffer interface` – Nobbie Nov 28 '15 at 21:16
edited to be compatibile with python3 – kwarunek Nov 28 '15 at 21:20

score -1 · Answer 2 · answered Nov 28 '15 at 20:37

Not sure what are you trying to do but here is one working example:

import sys

# print('Number of arguments:', len(sys.argv), 'arguments.')
# print('Argument List:', str(sys.argv))

# print(sys.argv[1])
# print(sys.argv[2])

a = int(sys.argv[1])
b = int(sys.argv[2])

print(a+b)

And your main_script.py:

import subprocess

try:

  out = subprocess.check_output(['python', 'test_script.py', "2", "3"], stderr=subprocess.STDOUT)
  print(out)

except subprocess.CalledProcessError as e:
  print(e.output)

This works but it uses `sys.argv`, is there any way for this to work with `input()`, or to change `input()` to `sys.argv` — Nobbie, Nov 28 '15 at 20:55

score -1 · Answer 3 · answered Nov 28 '15 at 20:39

That is jot going to work, test_script.py expects for keyboard input not the argument.

If you want main_script.py to pass arguments to test_script.py you have to amend test_script.py below code should do the trick

import sys

args = sys.argv[1:]
for arg in args:
    print arg

otherwise you can chek argparse https://docs.python.org/2/library/argparse.html

Subprocess stdin input

3 Answers3