Return `iface` IPv4 addr or an error if `iface` does not exist

def interface_ip(iface):
    '''
    Return `iface` IPv4 addr or an error if `iface` does not exist
    '''
    iface_info, error = _get_iface_info(iface)

    if error is False:
        inet = iface_info.get(iface, {}).get('inet', None)
        return inet[0].get('address', '') if inet else ''
    else:
        return error