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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 keep(self, *cols):
 """ Limit the dataframe to some columns :param cols: names of the columns :type cols: str :example: ``ds.keep("Col 1", "Col 2")`` """

        try:
            self.df = self.df[list(cols)]
        except Exception as e:
            self.err(e, "Can not remove colums")
            return
        self.ok("Setting dataframe to columns", " ".join(cols))