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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 average(self, rows: List[Row], column: NumberColumn) -> Number: """ Takes a list of rows and a column and returns the mean of the values under that column in those rows. """

        cell_values = [row.values[column.name] for row in rows]
        if not cell_values:
            return 0.0  # type: ignore
        return sum(cell_values) / len(cell_values)