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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 tail(self, rows: int=5):
 """ Returns the main dataframe's tail :param rows: number of rows to print, defaults to 5 :param rows: int, optional :return: a pandas dataframe :rtype: pd.DataFrame :example: ``ds.tail()`` """

        if self.df is None:
            self.warning("Dataframe is empty: no tail available")
        return self.df.tail(rows)