Python translation capabilities

puzzle.py

"""
Decode a super-secret message
"""
import sys
from string import maketrans

# setup translation
in_wrds   = "abcdefghijklmnopqrstuvwxyz"
out_wrds  = "cdefghijklmnopqrstuvwxyzab"
trans_tbl = maketrans(in_wrds, out_wrds)

# now translate
if len(sys.argv) > 0:
  print sys.argv[1].translate(trans_tbl)
else:
  puzzle    = open("puzzle.txt", "r")
  for line in puzzle:
    print line.translate(trans_tbl)

puzzle.txt

g fmnc wms bgblr rpylqjyrc gr zw fylb. rfyrq ufyr amknsrcpq ypc dmp. bmgle gr gl zw fylb gq glcddgagclr ylb rfyr'q ufw rfgq rcvr gq qm jmle. sqgle qrpgle.kyicrpylq() gq pcamkkclbcb. lmu ynnjw ml rfc spj.

rotate.py

def rotate_letter(letter, pos):
  """
  Rotate a letter by n positions
  
  >>> rotate_letter('a', 2)
  'b'
  """
  if letter.isalpha():
    letter = letter.lower()
    chr(ord(letter) + 2)
    
    adjusted_pos = ord(letter) - ord('a') + pos
    mod_pos = adjusted_pos % 26
    return chr(mod_pos + 97)
  else:
    return letter
    
    
temp = ""
f = open('puzzle.txt', 'r')
for l in f:
  for c in l:
    temp += rotate_letter(c, 2)
print temp