Python子进程通信杀死了我的进程

Question

Why does communicate kill my process? I want an interactive process but communicate does something so that I cannot take raw_input any more in my process.

from sys import stdin 
from threading import Thread
from time import sleep

if __name__ == '__main__':
    print("Still Running\n")
    x = raw_input()    
    i = 0
    while ('n' not in x ) :
        print("Still Running " + str(i) + " \r\n")
        x = raw_input()
        i += 1

    print("quit")



print(aSubProc.theProcess.communicate('y'))
print(aSubProc.theProcess.communicate('y'))

exception!

self.stdin.write(input)
ValueError: I/O operation on closed file

Answer 1

communicate and wait methods of Popen objects, close the PIPE after the process returns. If you want stay in communication with the process try something like this:

import subprocess
proc = subprocess.Popen("some_process", stdout=subprocess.PIPE, stdin=subprocess.PIPE)
proc.stdin.write("input")
proc.stdout.readline()

Answer 2

Why does communicate kill my process?

From the docs for Popen.communicate(input=None, timeout=None) :

Interact with process: Send data to stdin. Read data from stdout and
stderr, until end-of-file is reached. Wait for process to terminate. ^{emphasize mine}

You may call .communicate() only once. It means that you should provide all input at once:

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

p = Popen([sys.executable, 'child.py'], stdin=PIPE, stdout=PIPE)
print p.communicate(os.linesep.join('yyn'))[0]

Output

Still Running

Still Running 0 

Still Running 1 

quit

Notice the doubled newlines: one from '\\r\\n' and another from print statement itself in your script for the child process.

Output shows that the child process received three input lines successfully ( 'y' , 'y' , and 'n' ).

Here's a similar code using subprocess.check_output() 's input parameter from Python3.4:

#!/usr/bin/env python3.4
import os
import sys
from subprocess import check_output

output = check_output(['python2', 'child.py'], universal_newlines=True,
                      input='\n'.join('yyn'))
print(output, end='')

It produces the same output.

---

If you want to provide a different input depending on responses from the child processes then use pexpect module or its analogs to avoid issues mentioned in Why not just use a pipe (popen())?