def validate(self, value):
        super(Date, self).validate(value)

        if not (value is None or isinstance(value, (datetime.date,) + string_types + (float,) + bokeh_integer_types)):
            raise ValueError(value % "expected a date, string or timestamp, got %r")
dataset/ETHPy150Open bokeh/bokeh/bokeh/core/properties.py/Date.validate/swapped operands of `%`