Question

I’m trying to resolve a list of hostnames. The problem is when I hit a non existent domain, it slows down the whole process. The code is a trivial for loop:

for domain in domains:
    try:
        if socket.gethostbyname(domain.split('@')[1]):
            file1.write(domain)
        else:
            file2.write(domain)
    except socket.gaierror:
        pass

I was wondering if there is a simple way to parallelize what is inside the for loop.

Answer 1

You could use one of example from Gevent – dns_mass_resolve.py. There’s also usefull possibility of setting timeout for all queries.

from __future__ import with_statement
import sys
import gevent
from gevent import socket
from gevent.pool import Pool

N = 1000
# limit ourselves to max 10 simultaneous outstanding requests
pool = Pool(10)
finished = 0


def job(url):
    global finished
    try:
        try:
            ip = socket.gethostbyname(url)
            print ('%s = %s' % (url, ip))
        except socket.gaierror:
            ex = sys.exc_info()[1]
            print ('%s failed with %s' % (url, ex))
    finally:
        finished += 1

with gevent.Timeout(2, False):
    for x in xrange(10, 10 + N):
        pool.spawn(job, '%s.com' % x)
    pool.join()

print ('finished within 2 seconds: %s/%s' % (finished, N))