'Mark every hour in *byhour*; *byhour* can be an int or sequence.
Default is to tick every hour: ``byhour=range(24)``
*interval* is the interval between each iteration.  For
example, if ``interval=2``, mark every second occurrence.'

def __init__(self, byhour=None, interval=1, tz=None):

    if (byhour is None):
        byhour = range(24)
    rule = rrulewrapper(HOURLY, byhour=byhour, interval=interval, byminute=0, bysecond=0)
    RRuleLocator.__init__(self, rule, tz)
