y</var> is of
                an inappropriate type, <tt class="exception">TypeError</tt>
                may be raised; if of a value outside the set of indexes for
                the sequence (after any special interpretation of negative
                values), <tt class="exception">IndexError</tt> should be
                raised. <span class="note"><b class="label">Note:</b>
                <tt class="keyword">for</tt> loops expect that an <tt class=
                "exception">IndexError</tt> will be