Replaces the value with an appropriate interval symbol, if available.

def _discretize_check(self, table, att, col):
        '''
        Replaces the value with an appropriate interval symbol, if available.
        '''
        label = "'%s'" % col
        if table in self.discr_intervals and att in self.discr_intervals[table]:
            intervals = self.discr_intervals[table][att]
            n_intervals = len(intervals)

            prev_value = None
            for i, value in enumerate(intervals):

                if i > 0:
                    prev_value = intervals[i - 1]

                if not prev_value and col <= value:
                    label = "'=<%.2f'" % value
                    break
                elif prev_value and col <= value:
                    label = "'(%.2f;%.2f]'" % (prev_value, value)
                    break
                elif col > value and i == n_intervals - 1:
                    label = "'>%.2f'" % value
                    break
        else:
            # For some reason using [ and ] crashes TreeLiker
            label = label.replace('[', 'I')
            label = label.replace(']', 'I')

        return label