Recipe –Calfiles- persistency
		from astro.main.BiasFrame import BiasFrame class Bias(Cluster):     def __init__(self):         Cluster.__init__(self)     def make(self, targetname, previous_bias, raw_bias_list):         '''Make a master bias image         targetname -- pathname of master bias image         previous_bias -- pathname of previous bias         raw_bias_list -- pathnames of input raw biases