docs: def _upload(self, items: Iterable[Tuple[str, str]]) -> None:
          """
          Upload a collection of paths to S3.
  
          :param items: An iterable of pairs containing the local path of the
                        file to upload, and the remote path to upload it to. The
                        prefix will be appended to each remote path.
          """
          for src, key in items:
              logger.info(f'Uploading {src} to {key}')
              mimetype, _ = mimetypes.guess_type(src)
              if mimetype is None:
                  logger.warning(f'Could not guess MIME type for {src}')
                  mimetype = 'application/octet-stream'
  
              logger.debug(f'Deduced MIME type: {mimetype}')
              self._bucket.upload_file(src, key, ExtraArgs={
                      'ContentType': mimetype
                  })