code: def log_start_finish(msg, logger, level=logging.DEBUG):
      
      logger.log(level, 'start: ' + msg)
      yield
      logger.log(level, 'finish: ' + msg)
docs: A context manager to log messages with "start: " and "finish: "
      prefixes before and after a block.
  
      Parameters
      ----------
      msg : str
          Will be prefixed with "start: " and "finish: ".
      logger : logging.Logger
      level : int, optional
          Level at which to log, passed to ``logger.log``.