def validate_default_value(handler, default, norm, param='value'):
    """
    assert helper that quickly validates default value.
    designed to get out of the way and reduce overhead when asserts are stripped.
    """
    assert default is not None, '%s lacks default %s' % (handler.name, param)
    assert norm(default) == default, '%s: invalid default %s: %r' % (handler
        .name, param, default)
    return True
