code">rindex_from_opt&nbsp;s&nbsp;i&nbsp;c</code> returns the index of the last occurrence
    of byte <code class="code">c</code> in <code class="code">s</code> before position <code class="code">i+1</code> or <code class="code"><span class="constructor">None</span></code> if <code class="code">c</code> does not
    occur in <code class="code">s</code> before position <code class="code">i+1</code>.  <code class="code">rindex_opt&nbsp;s&nbsp;c</code> is equivalent to
    <code class="code">rindex_from&nbsp;