code: def _read_cache(self):
          
          if os.path.exists(self.filepath):
              with open(self.filepath, 'rt', encoding='utf8') as fh:
                  lines = [x.strip() for x in fh]
          else:
              logger.debug("Index not found, starting empty")
              lines = []
          return lines
docs: Read virtualenv metadata from cache.