print an /etc/hosts file to stdout with ec2 instances

ec2_hosts.py

#! /usr/bin/env python 
# ##########
#
# Usage:
#     ec2_hosts.py 
#
# Then copy results to /etc/hosts
#
# ##########

import re
import shutil
import subprocess

process = subprocess.Popen('ec2-describe-instances | grep ^INSTANCE | grep running | cut -f 2,4,5,17,18', shell=True, stdout=subprocess.PIPE)
stdout_value = process.communicate()[0]

host_lines = []
for line in stdout_value.split('\n'):
    try:
        (instance, external_dns, internal_dns, external_ip, internal_ip) = line.split();
        external_name,internal_name = external_ip,internal_ip
        external_name = 'ec2-' + external_name.replace('.', '-')
        internal_name = 'ip-' + internal_name.replace('.', '-')
        host_line = '%s\t%s %s %s %s %s' % (external_ip, instance, internal_name, external_name, internal_dns, external_dns)
        host_lines.append(host_line)
    except: 
        pass

new_ec2_part = '# EC2_HOSTS\n%s\n# END_EC2_HOSTS\n' % ('\n'.join(host_lines))

ec2_re = re.compile('^# EC2_HOSTS$.*# END_EC2_HOSTS', re.DOTALL|re.MULTILINE)
hosts_file = open('/etc/hosts').read()
new_hosts_file = ec2_re.sub(new_ec2_part, hosts_file)

shutil.copyfile('/etc/hosts', '/tmp/hosts')
print new_hosts_file