If you open a Python interpreter, and type \"import this\", as you know, it prints:
The Zen of Python, by Tim Peters
Beautiful is better
It uses ROT13 encoding. This is used because it's a joke.
You can also use Python functions to decode string.
Python 2 only:
import this
print(this.s.decode('rot13'))
Python 2 & 3:
import codecs
print(codecs.decode(this.s, 'rot-13'))
It's a substitution cipher (as mentioned in previous answers). Historically speaking, it's the Caesar cipher.
https://www.google.de/search?q=caesar+cipher&cad=h
If you want to make the ROT13 substitution by hand - or in your head - you can check that because 13*2 = 26 (the number of the letters of the English alphabet), it's essentially an interchange:
a <-> n
b <-> o
c <-> p
...
m <-> z
A <-> N
B <-> O
C <-> P
...
M <-> Z
Vs lbh cenpgvfr ybat rabhtu, lbh'yy riraghnyyl znfgre gur Mra bs EBG-13 nytbevguz naq ernq guvf Xyvatba ybbxvat grkgf jvgubhg pbzchgre uryc.
This is called rot13 encoding:
d = {}
for c in (65, 97):
for i in range(26):
d[chr(i+c)] = chr((i+13) % 26 + c)
Builds the translation table, for both uppercase (this is what 65 is for) and lowercase (this is what 97 is for) chars.
print "".join([d.get(c, c) for c in s])
Prints the translated string.
It's a substitution cipher, rot13.