Doc/tools/templates/customsourcelink.html

{%- if show_source and has_source and sourcename %}
  <div role="note" aria-label="source link">
    <h3>{{ _('This Page') }}</h3>
    <ul class="this-page-menu">
      <li><a href="{{ pathto('bugs') }}">{% trans %}Report a Bug{% endtrans %}</a></li>
      <li>
        <a href="https://github.com/python/cpython/blob/master/Doc/{{ sourcename|replace('txt', 'rst') }}"
            rel="nofollow">{{ _('Show Source') }}
        </a>
      </li>
    </ul>
  </div>
{%- endif %}