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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 renumber(self):
 """Re-number cells."""


        num = 0
        for cell in self.cells:
            cell_split = cell.splitlines()
            if len(cell_split) >= 2:
                num += 1
                cell_split[0] = str(num)
                yield '\n'.join(cell_split)