code: def _get_pages(self, locations, project_name):
          # type: (Iterable[Link], str) -> Iterable[HTMLPage]
          
          seen = set()  # type: Set[Link]
          for location in locations:
              if location in seen:
                  continue
              seen.add(location)
  
              page = _get_html_page(location, session=self.session)
              if page is None:
                  continue
  
              yield page
docs: Yields (page, page_url) from the given locations, skipping
          locations that have errors.