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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 rename(self, data, variables=None):
 """ Renames the columns according the variable mapping. Parameters data: DataFrame variables: None or dict, default None If None, uses self.variables Returns ------- data: DataFrame Renamed data. """

        if variables is None:
            variables = self.variables
        return data.rename(columns={y: x for x, y in variables.items()})