code: def _read_keyvals(filename):
          
          assert isinstance(filename, str)
          if os.path.exists(filename):
              return _KeyValuePersister._actually_populate_keyvals(filename)
          else:
              return {}
docs: Read the key/values if the file exists.
  
          returns -- a dictionary with key/values, or empty dictionary if the
                     file does not exist.