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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 stats(self):
 """ Return statistics calculated overall features in the container. Note: The feature container has to be opened in advance. Returns: DataStats: Statistics overall data points of all features. """

        self.raise_error_if_not_open()

        per_key_stats = self.stats_per_key()

        return stats.DataStats.concatenate(per_key_stats.values())