delastelle cipher in python

delastelle.py

from itertools import product

key = "EPSDUCVWYM ZLKXNBTFGORIJHAQ"

IND2L = dict(zip(list(product((1,2,3),repeat=3)),key))
L2IND = dict(zip(key,list(product((1,2,3),repeat=3))))

ptext = 'DEFEND THE EAST WALL OF THE CASTLE'
ctext = ""
for c in ptext:
    ctext += ''.join([str(i) for i in L2IND[c]])
    
print ctext

ptext2 = ""
for i in range(0,len(ctext),3):
    ind = tuple([int(ctext[i+k]) for k in [0,1,2]])
    ptext2 += IND2L[ind]
    
print ptext2