rot13 in Python 3.x

30th January 2009, 01:50 am

As of Python 3.0, rot13 is no longer built accessible from the str.encode("rot13") call. If needed, here is an implementation I pieced together:

from string import ascii_uppercase, ascii_lowercase
 
def rot13(data):
    """ A simple rot-13 encoder since `str.encode('rot13')` was removed from
        Python as of version 3.0.  It rotates both uppercase and lowercase letters individually.
    """
    total = []
    for char in data:
        if char in ascii_uppercase:
            index = (ascii_uppercase.find(char) + 13) % 26
            total.append(ascii_uppercase[index])
        elif char in ascii_lowercase:
            index = (ascii_lowercase.find(char) + 13) % 26
            total.append(ascii_lowercase[index])
        else:
            total.append(char)
    return "".join(total)

Pretty simple, right? Knowing how modulus (%) works helped greatly in finding the proper index. I hope this helps.

Update: There’s a simpler solution on the comments below. You should probably use it instead.

5 Comments

30 January 2009, 3:14 am

James Bennett wrote,

Simpler and probably more efficient:

rot13_trans = str.maketrans('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz', 'NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm')
 
def rot13(text):
    return text.translate(rot13_trans)

30 January 2009, 1:13 pm

Zack C wrote,

@James

My knee jerk reaction was to want to use string.ascii_uppercase/lowercase, but it doesn’t beat yours in terms of brevity or clarity.

from string import ascii_uppercase as uc, ascii_lowercase as lc
rot = uc[13:]+uc[:13] + lc[13:]+lc[:13]
rot13_trans = str.maketrans(uc+lc, rot)
def rot13(text):
    return text.translate(rot13_trans)

9 February 2010, 12:53 pm
iDontGiveMyNameToRandomSitesOnTheInternet wrote,

The simplest way to do this would probably be:
```
import codecs
codecs.encode("text to be rot13()'ed", "rot13")
```
12 December 2010, 1:53 pm
t|mm| wrote,

James Bennet’s version is the way I would have done it. So simple!!
16 January 2012, 8:21 am
Adam Ziaja wrote,

#!/usr/bin/env python
# -*- coding: rot13 -*-
cevag “Uryyb fgnpxbiresybj!”.rapbqr(“rot13″)