transpose in Python

my_gen_tab.py

import sys


STRING_COUNT = 6


def tab_column(fret, string):
    return (['---'] * (string - 1) +
            [fret.ljust(3, '-')] +
            ['---'] * (STRING_COUNT - string))


def tab_line(line):
    (string, fret) = line.split()
    return tab_column(fret, int(string))


for l in zip(*[tab_line(line) for line in sys.stdin]):
    print(''.join(l))