def switch(self):
base_block = self.base_block or self<EOL>self.next_block = Block(<EOL>self.parent, base_block=base_block, py3_wrapper=self.py3_wrapper<EOL>)<EOL>return self.next_block<EOL>
block has been split via | so we need to start a new block for that
option and return it to the user.