An algorithm of Permutation in DNA Computing

import copy

words = range(0, 3)

words = [str(e+1) for e in words]

n = len( words )

tubes = []

for i in range(n):

    tubes.append( [''] )

numTubes = len(tubes)

for i in range(n):

    for j in range(numTubes):

        for k in range(len(tubes[j])):

            tubes[j][k] += words[j]

    print tubes

    sumTube = []

    for j in range(numTubes):

        for e in tubes[j]:

            sumTube.append( e )

    for j in range(n):

        tubes[j] = copy.deepcopy( sumTube )