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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 _index(self, row):
 """Add a row to the internal list of rows without writing it to disk. This function should keep the data structure consistent so it's usable for both adding new rows, and loading pre-existing histories. """

        self.rows.append(row)
        self._keys.update(row.keys())
        self._steps += 1