I simplified @plaes answer (see below). Still recursive but easier to read and handles top-level lists/dicts, as well as mixed dict/list/suds combinations.

def pycast(o):
    if hasattr(o, '__keylist__'):
        return {k:pycast(v) for k,v in asdict(o).items()}
    elif isinstance(o, dict):
        return {k:pycast(v) for k,v in o.items()}
    elif isinstance(o, list):
        return [pycast(x) for x in o]
    else:
        return o