multiple procs w/o threading/multiprocessing

'''
pwait2.py -- multiple subprocesses without threading/multiprocessing
'''

import random, time
from subprocess import Popen


def work_diligently():
    cmd = ["/bin/sleep", str(random.randrange(2,4))]
    proc = Popen(cmd)
    print '\t{}\t{}'.format(proc.pid, cmd) # pylint: disable=E1101
    return proc


def spawn(num):
    return [ work_diligently() for _ in xrange(num) ]


# keep a 'pool' of NUM_PROCS Popen's running at one time
NUM_PROCS = 3
procs = spawn(NUM_PROCS)
while True:
    print time.ctime(), 'scan'
    procs = [
        proc for proc in procs
        if proc.poll() is None
    ]
    num_exited = NUM_PROCS - len(procs)
    if num_exited:
        print 'Uhoh! Restarting {} procs'.format(num_exited)
        procs.extend( spawn(num_exited) )
    time.sleep(1)