dynamic_inventory.py

#!/usr/bin/python

import json
import sys

inventory = {}
inventory['www'] = {}
inventory['www']['hosts'] = ['aaa.bbb.ccc.ddd']

if "--host" in sys.argv:
    if "aaa.bbb.ccc.ddd" in sys.argv:
        print json.dumps({'ansible_ssh_user': 'user', 'ansible_ssh_private_key_file': '/home/user/.ssh/user_common.pem'})
    else:
        print json.dumps({})
else:
    print json.dumps(inventory)