def _getBlocks(self, a, b):
        """Pass two zero based numbers and get two
        block objects. All checking done, returns (None, None)
        if the indexes are wrong
        """
        if not (0 < a < self.stacks.blockCount): return None, None
        if not (0 < b < self.stacks.blockCount): return None, None
        a = self.stacks.blocks[a]
        b = self.stacks.blocks[b]
        if a.position == b.position: return None, None
        return a, b
Pass two zero based numbers and get two
        block objects. All checking done, returns (None, None)
        if the indexes are wrong
        
recipes/Python/361168_Vpython_example/recipe-361168.py