How tp stop reading process without be hanged at the code in Python?

[Barakat]

Hi all

I have a Python program looks like this one :

import os
import time

process = os.popen("top").readlines()

time.sleep(1)

os.popen("killall top")

print process

the program hangs in :

process = os.popen("top").readlines()

because "Top" tool and that happens in the tools that keep update outputting

my best trials :

import os
import time
import subprocess

process = subprocess.Popen('top')

time.sleep(2)

os.popen("killall top")

print process

it worked better than the first one (it's kelled ), but it returns :

<subprocess.Popen object at 0x97a50cc>

the second trial :

import os
import time
import subprocess

process = subprocess.Popen('top').readlines()

time.sleep(2)

os.popen("killall top")

print process

the same as the first one. It hanged due to "readlines()"
...

I want its return like this :

top - 05:31:15 up 12:12,  5 users,  load average: 0.25, 0.14, 0.11
Tasks: 174 total,   2 running, 172 sleeping,   0 stopped,   0 zombie
Cpu(s):  9.3%us,  3.8%sy,  0.1%ni, 85.9%id,  0.9%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   1992828k total,  1849456k used,   143372k free,   233048k buffers
Swap:  4602876k total,        0k used,  4602876k free,  1122780k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND            
31735 Barakat   20   0  246m  52m  20m S 19.4  2.7  13:54.91 totem              
 1907 root      20   0 91264  45m  15m S  1.9  2.3  38:54.14 Xorg               
 2138 Barakat   20   0 17356 5368 4284 S  1.9  0.3   3:00.15 at-spi-registry    
 2164 Barakat    9 -11  164m 7372 6252 S  1.9  0.4   2:54.58 pulseaudio         
 2394 Barakat   20   0 27212 9792 8256 S  1.9  0.5   6:01.48 multiload-apple    
 6498 Barakat   20   0 56364  30m  18m S  1.9  1.6   0:03.38 pyshell            
    1 root      20   0  2880 1416 1208 S  0.0  0.1   0:02.02 init               
    2 root      20   0     0    0    0 S  0.0  0.0   0:00.02 kthreadd           
    3 root      RT   0     0    0    0 S  0.0  0.0   0:00.12 migration/0        
    4 root      20   0     0    0    0 S  0.0  0.0   0:02.07 ksoftirqd/0        
    5 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 watchdog/0         
    9 root      20   0     0    0    0 S  0.0  0.0   0:01.43 events/0           
   11 root      20   0     0    0    0 S  0.0  0.0   0:00.00 cpuset             
   12 root      20   0     0    0    0 S  0.0  0.0   0:00.02 khelper            
   13 root      20   0     0    0    0 S  0.0  0.0   0:00.00 netns              
   14 root      20   0     0    0    0 S  0.0  0.0   0:00.00 async/mgr          
   15 root      20   0     0    0    0 S  0.0  0.0   0:00.00 pm

and save in the variable "process". Any I idea guys ?

[coopstah13]

first off, don't use os.popen since its deprecated call

second, subprocess.popen returns a process object, so if you want output in there, you will have to change what you do

capturing output from top is hard, because of the nature of the application

17.1. subprocess ? Subprocess management — Python v2.7.1 documentation

[Barakat]

thanks coopstah13 for the replay, the problem has been solved :

import os
import subprocess
import time

subprocess.Popen("top >> tmp_file",shell = True)

time.sleep(1)

os.popen("killall top")

process = os.popen("cat tmp_file").read()

os.popen("rm tmp_file")

print process

and this is a much better code by ( J.F. Sebastian ) :

import collections
import subprocess
import time
import threading

def read_output(process, append):
	for line in iter(process.stdout.readline, ""):
		append(line)

def main():
	# start process, redirect stdout
	process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True)
	try:
        # save last `number_of_lines` lines of the process output
		number_of_lines = 200
		q = collections.deque(maxlen=number_of_lines) # atomic .append()
		t = threading.Thread(target=read_output, args=(process, q.append))
		t.daemon = True
		t.start()

		#
		time.sleep(2)
	finally:
		process.terminate() #NOTE: it doesn't ensure the process termination

	# print saved lines
	print ''.join(q)

if __name__=="__main__":
    main()