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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 gmean_(self, col: str, index_col: bool=True) -> "Ds": """ Group by and mean column :param col: column to group :type col: str :param index_col: :type index_col: bool :return: a dataswim instance :rtype: Ds :example: ``ds2 = ds.gmean("Col 1")`` """

        try:
            df = self.df.copy()
            df = df.groupby([col]).mean()
            if index_col is True:
                df[col] = df.index.values
            return self._duplicate_(df)
        except Exception as e:
            self.err(e, self.gmean_, "Can not meansum column")