rot13 in a more Pythonic style?

[Andy Dingley]

I'm trying to write rot13, but to do it in a better and more Pythonic
style than I'm currrently using. What would  you reckon to the
following pretty ugly thing?   How would you improve it?  In
particular, I don't like the way a three-way selection is done by
nesting two binary selections. Also I dislike stating the same
algorithm twice, but can't see how to parameterise them neatly.

Yes, I know of .encode() and .translate().
No, I don't actually need rot13 itself, it's just a convenient
substitute example for the real job-specific task.
No, I don't have to do it with lambdas, but it would be nice if the
final function was a lambda.


#!/bin/python
import string

lc_rot13 = lambda c : (chr((ord(c) - ord('a') + 13) % 26 + ord('a')))

uc_rot13 = lambda c : (chr((ord(c) - ord('A') + 13) % 26 + ord('A')))

c_rot13 = lambda c : (((c, uc_rot13(c)) [c in
'ABCDEFGHIJKLMNOPQRSTUVWXYZ']), lc_rot13(c) )[c in
'abcdefghijklmnopqrstuvwxyz']

rot13 = lambda s : string.join([ c_rot13(c) for c in s ],'')


print rot13( 'Sybevk Tenohaqnr, Fcyhaqvt ihe guevtt' )