code: def _add_redirects(self):
          
          html = '''
          <html>
              <head>
                  <meta http-equiv="refresh" content="0;URL={url}"/>
              </head>
              <body>
                  <p>
                      The page has been moved to <a href="{url}">{title}</a>
                  </p>
              </body>
          <html>
          '''
          with open(REDIRECTS_FILE) as mapping_fd:
              reader = csv.reader(mapping_fd)
              for row in reader:
                  if not row or row[0].strip().startswith('#'):
                      continue
  
                  path = os.path.join(BUILD_PATH,
                                      'html',
                                      *row[0].split('/')) + '.html'
  
                  try:
                      title = self._get_page_title(row[1])
                  except Exception:
                      # the file can be an ipynb and not an rst, or docutils
                      # may not be able to read the rst because it has some
                      # sphinx specific stuff
                      title = 'this page'
  
                  if os.path.exists(path):
                      raise RuntimeError((
                          'Redirection would overwrite an existing file: '
                          '{}').format(path))
  
                  with open(path, 'w') as moved_page_fd:
                      moved_page_fd.write(
                          html.format(url='{}.html'.format(row[1]),
                                      title=title))
docs: Create in the build directory an html file with a redirect,
          for every row in REDIRECTS_FILE.