I am trying to make a simple python script that starts a subprocess and monitors its standard output. Here is a snippet from the code:
process = subprocess.Popen([path_to_exe, os.path.join(temp_dir,temp_file)], stdout=subprocess.PIPE)
while True:
output=process.stdout.readline()
print "test"
The problem is that the script hangs on output=process.stdout.readline() and that the line print "test" only executes after the subprocess is terminated.
Is there a way to read standard output and print it without having to wait for the subprocess to terminate?
The subprocess which I am starting is a Windows binary for which I do not have the source code.
I have found several similar questions, but the answers are only applicable on Linux or in case I have the source of the suprocess I am starting.
解决方案
Check select module
import subprocess
import select
import time
x=subprocess.Popen(['/bin/bash','-c',"while true; do sleep 5; echo yes; done"],stdout=subprocess.PIPE)
y=select.poll()
y.register(x.stdout,select.POLLIN)
while True:
if y.poll(1):
print x.stdout.readline()
else:
print "nothing here"
time.sleep(1)
EDIT:
Threaded Solution for non posix systems:
import subprocess
from threading import Thread
import time
linebuffer=[]
x=subprocess.Popen(['/bin/bash','-c',"while true; do sleep 5; echo yes; done"],stdout=subprocess.PIPE)
def reader(f,buffer):
while True:
line=f.readline()
if line:
buffer.append(line)
else:
break
t=Thread(target=reader,args=(x.stdout,linebuffer))
t.daemon=True
t.start()
while True:
if linebuffer:
print linebuffer.pop(0)
else:
print "nothing here"
time.sleep(1)
