Short rot13 function - Python

Question

I am searching for a short and cool rot13 function in Python ;-) I've written this function:

def rot13(s):
    chars = "abcdefghijklmnopqrstuvwxyz"
    trans = chars[13:]+chars[:13]
    rot_char = lambda c: trans[chars.find(c)] if chars.find(c)>-1 else c
    return ''.join( rot_char(c) for c in s ) 

Can anyone make it better? E.g supporting uppercase characters.

Solution 1

maketrans()/translate() solutions…

Python 2.x

import string
rot13 = string.maketrans( 
    "ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz", 
    "NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm")
string.translate("Hello World!", rot13)
# 'Uryyb Jbeyq!'

Python 3.x

rot13 = str.maketrans(
    'ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz',
    'NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm')
'Hello World!'.translate(rot13)
# 'Uryyb Jbeyq!'

Solution 2

It's very simple:

>>> import codecs
>>> codecs.encode('foobar', 'rot_13')
'sbbone'

Solution 3

This works on Python 2 (but not Python 3):

>>> 'foobar'.encode('rot13')
'sbbone'

Solution 4

The maketrans and translate methods of str are handy for this type of thing.

Here's a general solution:

import string

def make_rot_n(n):
    lc = string.ascii_lowercase
    uc = string.ascii_uppercase
    trans = str.maketrans(lc + uc,
                          lc[n:] + lc[:n] + uc[n:] + uc[:n])
    return lambda s: str.translate(s, trans)

rot13 = make_rot_n(13)

rot13('foobar')
# 'sbbone'

Solution 5

From the builtin module this.py (import this):

s = "foobar"

d = {}
for c in (65, 97):
    for i in range(26):
        d[chr(i+c)] = chr((i+13) % 26 + c)

print("".join([d.get(c, c) for c in s]))  # sbbone

View more solutions

Comments

[Amber]

The .encode method is included as part of string objects and doesn't need to be specifically imported.

[svenwltr]

This is the shortest and its available under 3.0 :-)

[Youarefunny]

This appears to be the new proper way to do it. They moved it out of the string object for modularity. Now the string object str.encode() raises errors about not returning a byte array or bytes object.

[Admin]

But in Python 3, you need to spell it "rot_13" or "rot-13", not "rot13". I edited the answer.

[Wooble]

This no longer works on Python3.2+; maketrans was removed from the string module. Use Nazmul Hasan's codecs answer instead.

[Milo P]

Note also that this causes problems if you're trying to make Unicode text into rot13 and it contains any character larger than one byte (e.g., a non-breaking space).

[Jonathan Potter]

This doesn't work in Python 3, but @Nazmul's similar method does.

[kkessell]

Rumor: that's possibly just rot13 reading of a file as python source. See stackoverflow.com/a/1024693/26494

[Muposat]

for Python3.x: change to rot13 = str.maketrans(...) and then "Hello World!".translate(rot13)

[ankostis]

@steven-rumbalski Strange! In py3.5 I get this error: LookupError: 'rot13' is not a text encoding; use codecs.encode() to handle arbitrary codecs

[Brent Knox]

for Python3.x import string rot13 = str.maketrans( "ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz", "NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm") print(str.translate("Hello World!", rot13))

[wjandrea]

Doug's answer has a cleaner way of making a dict.

[김민준]

You can also directly import this. import this;rot13 = lambda s:''.join(this.d.get(c, c) for c in s). Just saying.

[Martijn Pieters]

@poke: it is definitely an available codec in Python 3. Just not as a str-to-bytes or bytes-to-str codec.

[Martijn Pieters]

@Amber: str.encode() can only produce bytes in Python 3. The rot13 codec is a str-to-str codec and is only available via codecs.encode() and codecs.decode().

[Martijn Pieters]

@user1220978: rot13 is available in 3.6 at the very least.

[Martijn Pieters]

@StevenRumbalski: if str.encode('rot13') ever worked in older 3.x releases then that was a mistake, as str.encode() is strict about producing bytes results only, while ROT13 is a text-to-text codec.

[Orsiris de Jong]

Your solution is elegant, but won't handle scenarios with accents (ie éêèö and alike) because str.isalpha() returns True for those characters. Here's a lightly modified version that does not use str.isalpha(): def rot13(s): return ''.join([chr(ord(n) + (13 if 'Z' < n < 'n' or n < 'N' else -13)) if ('a' <= n <= 'z' or 'A' <= n <= 'Z') else n for n in string])

[Boris Verkhovskiy]

@Ensemble the documentation says "New in version 3.2: Restoration of the rot_13 text transform." and "Changed in version 3.4: Restoration of the rot13 alias." So neither work on 3.0 and 3.1, then rot_13 works on 3.2 and 3.3 and then both rot_13 and rot13 work on 3.4+ (as well as Python 2).

[pat]

Same idea with basic python: def rot13(s): m = {a:b for a,b in zip("ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz", "NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm")} return ''.join(m.setdefault(c, c) for c in s)

[MadMad666]

I liked it, very interesting way to do.