<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def load_inventory(hosts_file=HOSTS_FILE):
    '''Loads Ansible inventory from file.

    Parameters
    ----------
    hosts_file: str, optional
        path to Ansible hosts file

    Returns
    -------
    ConfigParser.SafeConfigParser
        content of `hosts_file`
    '''
    inventory = SafeConfigParser(allow_no_value=True)
    if os.path.exists(hosts_file):
        inventory.read(hosts_file)
    else:
        logger.warn('inventory file doesn\'t exist: %s', hosts_file)
    return inventory