stopall.py

import subprocess
import signal
import os

#Get all proceses owned by group "download"
proc = subprocess.Popen(["ps","-G","download"], bufsize=-1, stdout=subprocess.PIPE)

for line in proc.stdout: #Do this for each printed line of the above command
        try:
                fields = line.split()   #Split the line according to spaces
                pid = fields[0]         #The first field is the PID of the process (field 4 is the name of it)
                if int(pid) > 0:        #If its a positive number
                        os.kill(int(pid), signal.SIGSTOP)       #Send SIGSTOP to PID
        except:
                continue                #If any problem, continue with the next line