def deselect_by_index(self, index):
        """Deselect the option at the given index. This is done by examing the "index" attribute of an
           element, and not merely by counting.

           :Args:
            - index - The option at this index will be deselected

            throws NoSuchElementException If there is no option with specified index in SELECT
        """
        if not self.is_multiple:
            raise NotImplementedError("You may only deselect options of a multi-select")
        for opt in self.options:
            if opt.get_attribute("index") == str(index):
                self._unsetSelected(opt)
                return
        raise NoSuchElementException("Could not locate element with index %d" % index)