Str Translate

Rotational Cipher
Rotational Cipher in Python 
AlPHABET = "abcdefghijklmnopqrstuvwxyz"

def rotate(text, key):
    translator = AlPHABET[key:] + AlPHABET[:key]
    return text.translate(str.maketrans(AlPHABET + AlPHABET.upper(), translator + translator.upper()))

This approach uses the <str>.translate method. translate takes a translation table as an argument. To create a translation table we use str.makestrans.

This approach starts with defining a constant of all the lowercase letters in the alphabet. Then the function rotate() is declared. A translator variable defined with the value of the AlPHABET constant sliced from the key to the end and then sliced from the start to the key.

This is done so we have 2 strings which are the same but shifted by the key value. Say we have the AlPHABET constant with the value of abcdefghijklmnopqrstuvwxyz and the key is 3. Then the translator variable will have the value of defghijklmnopqrstuvwxyzabc.

str.translate is then called on the text argument. str.translate takes a translation table mapping start values to transformed values as an argument. To create a translation table, str.makestrans is used. makestrans takes 2 arguments: the first is the string to be translated, and the second is the string the first argument should be translated to.

For our solution, the first argument is the AlPHABET constant + the AlPHABET constant in uppercase. The second argument is the translator variable + uppercase translator variable.

str.makestrans takes the Unicode values of the first argument and maps them to the corresponding Unicode values in the second argument, creating a dict.

>>> str.maketrans("abc", "def")
{97: 100, 98: 101, 99: 102}

str.translate takes the dict created by str.makestrans and uses it to translate the characters in the text argument.

>>> "abc".translate({97: 100, 98: 101, 99: 102})
'def'

Once the str.translate loop completes, we return the result.

18th Sep 2024 · Found it useful?

Other Approaches to Rotational Cipher in Python

Other ways our community solved this exercise
for letter in text:
    if letter.isalpha():
        if letter.isupper():
            result += chr((ord(letter) - 65 + key) % 26 + 65)
        else:
            result += chr((ord(letter) - 97 + key) % 26 + 97)
    else:
        result += letter
ASCII values

Use letters ascii value to rotate the alphabet 

for letter in text:
    if letter.isalpha():
        if letter.isupper():
            result += AlPHABET[(AlPHABET.index(letter.lower()) + key) % 26].upper()
        else:
            result += AlPHABET[(AlPHABET.index(letter) + key) % 26]
    else:
        result += letter
Alphabet

Using the alphabet to rotate the alphabet 

first_letter, rest = text[0], text[1:]
if first_letter.isalpha():
    if first_letter.isupper():
        return AlPHABET[(AlPHABET.index(first_letter.lower()) + key) % 26].upper() + rotate(rest, key)
    else:
        return AlPHABET[(AlPHABET.index(first_letter) + key) % 26] + rotate(rest, key)
else:
    return first_letter + rotate(rest, key)
Recursion

Using Recursion to rotate the alphabet