Decode python rot13 string

Question

I've a rot13 encoded string in python and I've to decode it:

"Gur dhvpx oebja sbk whzcrq bire gur ynml qbt"

Is it possible to do in python? I can't find any method to do it.

Please help!

This is what I've tried:

s = "Gur dhvpx oebja sbk whzcrq bire gur ynml qbt"
s1 = ""
for i in range(len(s)):
    c = s[i]
    if c >= 'a' and c <= 'm': c += 13
    elif c > 'A' and c < 'M': c += 13
    elif c >= 'n' and c < 'z': c -= 13
    elif c >= 'N' and c <= 'Z': c -= 13
    s1 += c
    print(c)
print(s1)

No that is completely impossible. The fact that there is no method to do this also means that you can not do it yourself... :) — Willem Van Onsem, Oct 29 '17 at 16:23
nope, I need to decode rot13 encoded string not encode it @KlausD. — user8852303, Oct 29 '17 at 16:32
@user8852303: since the alphabet has 26 letters, encoding and decoding is exactly the same operation. — Willem Van Onsem, Oct 29 '17 at 16:33
Then i recommend that you get known to ROT13 at first. There will be a large surprise, I promise. You might also just give it a try. — Klaus D., Oct 29 '17 at 16:34
Is your code functional? If it's not, change every line of `c += 13` and `c -= 13 ` with `c = chr(ord(c) + 13)` and `c = chr(ord(c) - 13)` respectively. That should work. — Vasilis G., Oct 29 '17 at 16:36
Don't roll back my edit. There's no need for that sort of language (even hidden like that). — ChrisF, Oct 29 '17 at 19:04

score 2 · Accepted Answer · edited Oct 29 '17 at 19:04

To decode a rot13 encoded string, say s, simply take rot13 of the string once again, i.e. compute rot13(s).

If you are not familiar how to compute rot13 in python, try googling a bit and you'll surely find one. I googled and found a solution that works pretty well : https://stackoverflow.com/a/3269756/3293087 [Note that it works only on python2 and not python3 since string.maketrans was removed from python3.]

I'll write the code here for completeness :

# Python 2 solution
import string
rot13Table = string.maketrans( 
    "ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz", 
    "NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm")
rot13 = lambda s : string.translate(s, rot13Table)

print rot13("Hello World!") 
# Outputs "Uryyb Jbeyq!"

Note : I'm not going to write the decoded string corresponding to what the OP originally posted, since its quite offensive and homophobic. Anyone interested can do it themselves.

Update : I also found a solution that works for python 2 & 3 both from this SO answer. It turns out there is a builtin rot13 encoder in python in the codecs module :

# Python 2 & 3 compatible
import codecs
rot13 = lambda s : codecs.getencoder("rot-13")(s)[0]

# Answer
rot13("Gur dhvpx oebja sbk whzcrq bire gur ynml qbt")

Update 2 : Since the OP is adamant to know the answer and does not seem to have python installed, I have a created JS solution https://codepen.io/anon/pen/zPYVQP. Others please proceed with caution.

take rot13 again, thanks for the great explanation @AbhishekKedia, i would appreciate if you could post the output as well. thanks again. — user8852303, Oct 29 '17 at 17:22
The `string` library has been replaced with the `str` global in Python 3. — Nick McCurdy, Mar 08 '23 at 14:13

score 0 · Answer 2 · edited Mar 08 '23 at 14:04

0

utf8 = str.maketrans(
    # this are the related alphabets
    "NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm",
    "ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz",
)  
print(str.translate("Gur dhvpx oebja sbk whzcrq bire gur ynml qbt", utf8))

edited Mar 08 '23 at 14:04

Nick McCurdy

17,658
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answered Oct 29 '17 at 16:42

Hello and welcome to SO. Its good to have a description along with the output of the code as mentioned above. – Ziyan Junaideen Oct 29 '17 at 17:01

Decode python rot13 string

2 Answers2