Deletes an index from the Table.  Can be used to drop and rebuild an index,
           or to convert a non-unique index to a unique index, or vice versa.
           @param attr: name of an indexed attribute
           @type attr: string

def delete_index(self, attr):
        """Deletes an index from the Table.  Can be used to drop and rebuild an index,
           or to convert a non-unique index to a unique index, or vice versa.
           @param attr: name of an indexed attribute
           @type attr: string
        """
        if attr in self._indexes:
            del self._indexes[attr]
            self._uniqueIndexes = [ind for ind in self._indexes.values() if ind.is_unique]
        return self