python subprocess Popen is not delivering stdin

Question

I know that similar questions have been asked many times, but I didn't manage to apply those solutions to my case.

I have this interactive program:

#!/bin/sh                                                                                                                                                                   

echo "banana"                                                                                                                                                               
while true                                                                                                                                                                  
do                                                                                                                                                                          
    read line                                                                                                                                                               
    echo $line                                                                                                                                                              
done

and I am trying to communicate with it via python, but this happens:

> python3
Python 3.3.1 (default, Apr 24 2013, 16:43:21) 
[GCC 4.7.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from subprocess import Popen,PIPE,STDOUT
>>> p = Popen("x.sh", stdin = PIPE, stdout = PIPE)
>>> print(p.stdout.readline())
b'banana\n'
>>> p.stdin.write(bytes('xyzgewgwer','UTF-8'))
10
>>> print(p.stdout.readline())

sometimes it hangs there, but sometimes it prints

b''

any idea?

Answer 1

You should use communicate and wait

Example:

import subprocess
cmd="x.sh"
prc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
prc.stdin.write("yo\n")
stdout, stderr = prc.communicate()
prc.wait()
print (stdout)