code: def _ParseFileVersion(file_version):
    
    tokens = file_version.split('brain.Event:')
    try:
      return float(tokens[-1])
    except ValueError:
      ## This should never happen according to the definition of file_version
      ## specified in event.proto.
      logger.warn(
          ('Invalid event.proto file_version. Defaulting to use of '
           'out-of-order event.step logic for purging expired events.'))
      return -1
docs: Convert the string file_version in event.proto into a float.
  
    Args:
      file_version: String file_version from event.proto
  
    Returns:
      Version number as a float.