Validate convertibility to internal representation

        Returns
        -------
        bool
          True if 'obj' matches the data type

        Raises
        -------
        ValidationError
            If the validation fails

def validate(self, obj):
        """Validate convertibility to internal representation

        Returns
        -------
        bool
          True if 'obj' matches the data type

        Raises
        -------
        ValidationError
            If the validation fails

        """
        if not isinstance(obj, self.internal_type):
            raise ValidationError(obj, self.internal_type)
        return True