Decorator converts function's arguments from dbus types to python.

def signal_wrapper(f):
    """Decorator converts function's arguments from dbus types to python."""
    @wraps(f)
    def wrapper(*args, **kwds):
        args = map(convert, args)
        kwds = {convert(k): convert(v) for k, v in kwds.items()}
        return f(*args, **kwds)
    return wrapper