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

        if value is None: return

        try:
            import json
            json.loads(value)
        except ValueError:
            raise ValueError(value % "expected JSON text, got %r")
dataset/ETHPy150Open bokeh/bokeh/bokeh/core/properties.py/JSON.validate/swapped operands of `%`