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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 fetchone(self):
 """Fetch the next row of a query result set, returning a single sequence, or ``None`` when no more data is available. """

        if self._state == self._STATE_NONE:
            raise Exception("No query yet")
        if not self._data:
            return None
        else:
            self._rownumber += 1
            return self._data.pop(0)