DEFAULT_POLICY_FILE = 'policy.yaml'
OLD_POLICY_FILE = 'policy.json'


def pick_file(policy_file):
 if policy_file:
    return policy file

 if CONF.policy_file == DEFAULT_POLICY_FILE:
     if os.path.exists(CONF.policy_file):
         return CONF.policy_file
 elif CONF.policy_file == OLD_POLICY_FILE:
     # Do this smarter
     json_backup = CONF.policy_file.replace('yaml', 'json')
     if os.path.exists(json_backup):
     return json_backup
 # Same behavior if no overrides
 return CONF.policy_file