Speed up Python script's for loop

Question

Assuming you got something like this (copied from here):

#!/usr/bin/python
from scapy.all import *

TIMEOUT = 2
conf.verb = 0
for ip in range(0, 256):
    packet = IP(dst="192.168.0." + str(ip), ttl=20)/ICMP()
    reply = sr1(packet, timeout=TIMEOUT)
    if not (reply is None):
         print reply.src, "is online"
    else:
         print "Timeout waiting for %s" % packet[IP].src

There is no need to wait for each ping to finish before trying the next host. Could I put the loop interior each time into the background along the lines of the & in:

for ip in 192.168.0.{0..255}; do 
ping -c 1 $ip &
done

Beside the point, but are you aware that `range(0,255)` ends at `254`? — Tim Pietzcker, Sep 16 '13 at 12:43
You could use the [`concurrent.futures`](http://docs.python.org/3/library/concurrent.futures.html#module-concurrent.futures) module to do pings concurrently. — Fred Foo, Sep 16 '13 at 12:48
You should use some asynchronous library, or select. Also, `reply is not None` looks better than `not (reply is None)`. ;) — Bunyk, Sep 16 '13 at 12:49
You can actually provide a range of IP addresses to capy, and it will send out accordingly, you can then evaluate the results of sr separately, which would work a lot faster as there should be less I/O blocks. — KillianDS, Sep 16 '13 at 12:52

score 5 · Accepted Answer · answered Sep 16 '13 at 12:49

The first thing you should do is change your range to range(0, 256) so that it is inclusive of 0-255.

Second, you're looking at Python's threading, which can be somewhat similar to Bash process daemonization at an abstract level.

Import multiprocessing and create a pool:

from multiprocessing.pool import ThreadPool
pool = ThreadPool(20)  # However many you wish to run in parallel

So take the ping lookup, which is everything inside of the for loop, and make it a function.

def ping(ip):
    packet = IP(dst="192.168.0." + str(ip), ttl=20)/ICMP()
    reply = sr1(packet, timeout=TIMEOUT)
    if not (reply is None):
         print reply.src, "is online"
    else:
         print "Timeout waiting for %s" % packet[IP].src

Then in your for loop,

for ip in range(0, 256):
    pool.apply_async(ping, (ip,))

pool.close()
pool.join()

pool.join() is what waits for all of your threads to return.

score 0 · Answer 2 · edited May 23 '17 at 11:50

0

You can use threading or multiprocessing module to run aynchronous/non-blocking IO calls.

Read about hte difference on SO:

multiprocess or threading in python?

edited May 23 '17 at 11:50

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answered Sep 16 '13 at 12:50

btel

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Speed up Python script's for loop

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