def __init__(self, instance_type, default=None, help=None):
        if not isinstance(instance_type, (type,) + string_types):
            raise ValueError("expected a type or string, got %s" % instance_type)

        if isinstance(instance_type, type) and not issubclass(instance_type, HasProps):
            raise ValueError("expected a subclass of HasProps, got %s" % instance_type)

        self._instance_type = instance_type

        super(Instance, self).__init__(default=default, help=help)
dataset/ETHPy150Open bokeh/bokeh/bokeh/core/properties.py/Instance.__init__/original