Gevent example with gethostbyname

example.py

#!/usr/bin/env python
import sys
import gevent
from gevent import socket

# lazy global variable for storing results
results = []

# greenlet worker
def worker(name):
    try:
        # this is an async version of gethostbyname
        res = socket.gethostbyname(name)
        results.append({"name": name, "ip": res})
    except socket.gaierror:
        pass

def main():
    domain = sys.argv[1]
    name_file = sys.argv[2]
    names = []
    with open(name_file) as f:
        names = f.readlines()
    names = ['{0}.{1}'.format(n.strip(), domain) for n in names]
    # normally would use a list comprehension but i wanted the example
    # to be clearer
    # for each name in names we spawn a greenlet
    jobs = []
    for name in names:
        jobs.append(gevent.spawn(worker, name))
    # wait for all the greenlets to complete
    gevent.joinall(jobs)
    for result in results:
        print 'Found  {0} => {1}'.format(result['name'], result['ip'])

if __name__ == '__main__':
    main()