 only be
            implemented for mappings if the objects support changes to the
            values for keys, or if new keys can be added, or for sequences if
            elements can be replaced. The same exceptions should be raised
            for improper <var>key</var> values as for the <tt class=
            "method">__getitem__()</tt> method.
          </dd>
        </dl>
        <dl>
          <dt>
            <b><a name="l2h-131"><tt class=
            "method">__delitem__</tt></a></b>(<var>self,