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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_both_blocks_sibling(self):
 """If this is a both-blocks activity, get the other EighthScheduledActivity object that occurs on the other block. both_blocks means A and B block, NOT all of the blocks on that day. Returns: EighthScheduledActivity object if found None if the activity cannot have a sibling False if not found """

        if not self.is_both_blocks():
            return None

        if self.block.block_letter and self.block.block_letter.upper() not in ["A", "B"]:
            # both_blocks is not currently implemented for blocks other than A and B
            return None

        other_instances = (EighthScheduledActivity.objects.filter(activity=self.activity, block__date=self.block.date))

        for inst in other_instances:
            if inst == self:
                continue

            if inst.block.block_letter in ["A", "B"]:
                return inst

        return None