':param stat: stat function. See ``os.stat`` for details.
:param listdir: listdir function. See ``os.listdir`` for details.
:type polling_interval: float
:param polling_interval: interval in seconds between polling the file system.'

def __init__(self, stat, listdir, polling_interval=1):

    emitter_cls = partial(PollingEmitter, stat=stat, listdir=listdir)
    BaseObserver.__init__(self, emitter_class=emitter_cls, timeout=polling_interval)
