Next point in iteration

def next(self):
        """Next point in iteration
        """
        while True:
            x, y = next(self.scan)
            self.index += 1
            if (self.index < self.start): continue
            if (self.index > self.stop): raise StopIteration("skip stopping")
            if ((self.index-self.start) % self.step != 0): continue
            return x, y