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

        if value is not None:
            if not (isinstance(value, dict) and \
                    all(self.keys_type.is_valid(key) and self.values_type.is_valid(val) for key, val in iteritems(value))):
                raise ValueError((self, value) % "expected an element of %s, got %r")
dataset/ETHPy150Open bokeh/bokeh/bokeh/core/properties.py/Dict.validate/swapped operands of `%`