Ansible module to list groups in inventory (Python version :D)

#! /bin/python
# 7 minutes Ansible module to list groups in inventory (Python version) :D
# You can print output like "pretty-print" outside Ansible by using:
#./listgroups /path/to/ansible.cfg | python -m json.tool 

import sys
import re
import json
 
#get hosts inventory from ansible.cfg file.
ansible_conf_file = open(sys.argv[1]).read()
hosts_file = re.findall('hostfile\s*=\s*(.*)', ansible_conf_file)[0]
 
#Get groups from inventory file and add it to array. 
cat_hosts_file = open(hosts_file).readlines()
group = 'Default' # for hosts without a group
groups_list = {group: 0}
for line in cat_hosts_file:

	# Skip comments & empty lines
	line = line.strip()
	if not line or line.startswith('#'):
		continue

	if line.startswith('['): # group
		group = re.sub(r'[\[\]]', '', line)
		groups_list[group] = 0
	else: # host
		groups_list[group] += 1
 
#Print output in json format.
print '{"Inventory Groups": ' + json.dumps(groups_list) + '}'

When I run the script I get:

python mtayseer_simplified_script.py ansible.cfg
Traceback (most recent call last):
File "mtayseer_simplified_script.py", line 15, in
cat_hosts_file = open(hosts_file).read()
IOError: [Errno 2] No such file or directory: '/etc/ansible/hosts'

---

ansible.cfg file looks like:

[defaults]

some basic default values...

hostfile

hostfile = /etc/ansible/hosts

hostfile = /tmp/hosts

---

Python version: 2.7.6
System: Ubuntu 14.04

Updated