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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 daterange(self, datecol, date_start, op, **args):
 """ Returns rows in a date range """

        df = self._daterange(datecol, date_start, op, **args)
        if df is None:
            self.err("Can not select date range data")
        self.df = df