Continuous interaction with subprocess in Python (Windows)

Question

I am starting a script in a new PowerShell window from python and I'd like to let that process run in the background, so I can interact with it continuously.

I've tried with the following code:

p = subprocess.Popen(['start powershell.exe', '-File', 'script.ps1']
                    shell    = True,
                    stdin    = subprocess.PIPE,
                    stdout   = subprocess.PIPE,
                    bufsize  = 1,
                    encoding ='utf-8')

p.stdin.write('input1')
p.stdout.readline()
p.stdin.write('input2')
p.stdout.readline()
p.stdin.write('input3')
p.stdout.readline()

But p.stdin.write does nothing. How can I solve this problem?

Does this answer your question? [How do I pass a string into subprocess.Popen (using the stdin argument)?](https://stackoverflow.com/questions/163542/how-do-i-pass-a-string-into-subprocess-popen-using-the-stdin-argument) — Maurice Meyer, Sep 16 '20 at 10:52
I've already tried with communicate(), but it does not support multiple communication — Lin, Sep 16 '20 at 11:19
*"I can interact with it continuously"* - What does that mean? — IInspectable, Sep 16 '20 at 13:02
@IInspectable like the code says: I have multiple inputs, I want to feed them to the subprocess sequentielly and get the result each time — Lin, Sep 16 '20 at 13:16

Hassan Voyeau · Accepted Answer · 2020-09-17T13:55:02.903

1

I have created a minimal example to understand exactly what you want. From this tell me what you want?

test.py

import subprocess, sys, os

p = subprocess.Popen(['start', 'powershell.exe', '-File', 'H:\Coding\stack\script.ps1'],
                    shell=True,
                    stdout = subprocess.PIPE,
                    stdin = subprocess.PIPE,
                    bufsize = 1,
                    encoding ='utf-8'
                    )

while p.poll() is None:
    output = p.stdout.readline()
    print(output)

print('end of python'))

script.ps1

$input = Read-Host -Prompt 'input'
Write-Host $input
$input = Read-Host -Prompt 'input'
Write-Host $input
$input = Read-Host -Prompt 'input'
Write-Host $input
Write-Host 'end of process'

Write-Host -NoNewLine 'Press any key to continue...';
$null = $Host.UI.RawUI.ReadKey('NoEcho,IncludeKeyDown');

Results

PS H:\Coding\stack> python test.py
(new window started)
input: test
test
input: this
this
input: out
out
end of process
Press any key to continue...
(window closed)
end of python

edited Sep 17 '20 at 13:55

answered Sep 16 '20 at 13:26

Hassan Voyeau

3,383
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Thanks for your effort. "start" is missing in front of "powershell.exe" since I need a separate window. I am not using p.communicate() because I have more than one input. – Lin Sep 16 '20 at 13:43
In another words, I have more than one "hello" as input, but "hello1", "hello2", "hello3" etc. and I need to process them sequentially – Lin Sep 16 '20 at 13:45
@Lin Updated answer – Hassan Voyeau Sep 16 '20 at 14:03
1

To get a separate console window, you can use `creationflags=subprocess.CREATE_NEW_CONSOLE` with `shell=False` (default) instead of CMD's internal `start` command with `shell=True`. There's no need to spawn a cmd.exe process for this. – Eryk Sun Sep 16 '20 at 20:00
Also, an args list shouldn't be used with `shell=True` anyway since subprocess doesn't know how to properly build a command line for cmd.exe (it doesn't use `CommandLineToArgvW` rules). Also, using `start` here is buggy if the path to the script ends up containing spaces since `start` will interpret the first quoted string, in this case the path, as the window title to use. – Eryk Sun Sep 16 '20 at 20:01

Continuous interaction with subprocess in Python (Windows)

1 Answers1