def pformat(self, prefix=()):
        '''
        Makes a pretty ASCII format of the data, suitable for
        displaying in a console or saving to a text file.
        Returns a list of lines.
        '''
        nan = float("nan")

        def sformat(segment, stat):
            FMT = "n={0}, mean={1}, p50/95={2}/{3}, max={4}"
            line_segs = [segment]
            for s in [stat]:
                p = s.get_percentiles()
                p50, p95 = p.get(0.50, nan), p.get(0.95, nan)
                line_segs.append(FMT.format(s.n, s.mean, p50, p95, s.max))
            return '{0}: {1}'.format(*line_segs)

        lines = []
        for path in sorted(self.path_stats.keys()):
            lines.append('=====================')
            for seg, stat in zip(path, self.path_stats[path]):
                lines.append(sformat(seg, stat))
        return lines
Makes a pretty ASCII format of the data, suitable for
        displaying in a console or saving to a text file.
        Returns a list of lines.