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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 count_unique_(self, field):
 """ Return the number of unique values in a column """

        try:
            num = self.df[field].nunique()
        except Exception as e:
            self.err(e, "Can not count unique values")
            return
        self.ok("Found", num, "unique values in column", field)