class PZero(GeneratorPattern):
   # crash server PZero function
     ''' Generate a Pattern with '1' and size-1 '0' 
            eg: PZero(5) -> P[1,0,0,0,0] 
            the '1' position can be offset 
            '''
        def __init__(self, size=2, offset=0):
            GeneratorPattern.__init__(self)
            self.size = size
            self.offset = offset
        def func(self, index):
            if ((index-self.offset)%int(self.size) == 0):
                return 1
            else:
                return 0