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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 mask(self):
 """ Create a mask implementing the requested filter on the datasets Returns ------- array of Boolean True for dataset indices to be returned by the get_column method """

        if self.filter_func is None:
            raise RuntimeError("Can't get a mask without a filter function!")
        else:
            # only evaluate if no previous calculation was done
            if self._mask is None:
                # get required columns into the namespace as numpy arrays
                for column in self.columns:
                    if column in self.filter_func:
                        setattr(self, column, self.group[column][:])
                self._mask = eval(self.filter_func)
            return self._mask