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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _add_log_handler( handler, level=None, fmt=None, datefmt=None, propagate=None):
 """ Add a logging handler to Orca. Parameters handler : logging.Handler subclass level : int, optional An optional logging level that will apply only to this stream handler. fmt : str, optional An optional format string that will be used for the log messages. datefmt : str, optional An optional format string for formatting dates in the log messages. propagate : bool, optional Whether the Orca logger should propagate. If None the propagation will not be modified, otherwise it will be set to this value. """

    if not fmt:
        fmt = US_LOG_FMT
    if not datefmt:
        datefmt = US_LOG_DATE_FMT

    handler.setFormatter(logging.Formatter(fmt=fmt, datefmt=datefmt))

    if level is not None:
        handler.setLevel(level)

    logger = logging.getLogger('orca')
    logger.addHandler(handler)

    if propagate is not None:
        logger.propagate = propagate