'Raise an exception on property access if unacknowledged.'

def _raise_if_unacknowledged(self, property_name):

    if (not self.__acknowledged):
        raise InvalidOperation(('A    value    for    %s    is    not    available    when    the    write    is    unacknowledged.    Check    the    acknowledged    attribute    to    avoid    this    error.' % (property_name,)))
