Getting Started(Chapter 1 of Python 2.6 Text Processing)

 1 import sys
 2 import string
 3 
 4 CHAR_MAP = dict(zip(string.ascii_lowercase, string.ascii_lowercase[13:26] +
 5                     string.ascii_lowercase[0:13]))
 6 
 7 def rotate13_letter(letter):
 8     """
 9     Return the 13-char rotation of a letter.
10     """
11     do_upper = False
12     if letter.isupper():
13         do_upper = True
14     letter = letter.lower()
15     if letter not in CHAR_MAP:
16         return letter
17     else:
18         letter = CHAR_MAP[letter]
19         if do_upper:
20             letter = letter.upper()
21     return letter
22 
23 if __name__ == '__main__':
24     for char in sys.argv[1]:
25         sys.stdout.write(rotate13_letter(char))
26     sys.stdout.write('\n')
27