Python Shift Cyphers

[Archenemie]

I have just started looking at simple cryptography in order to learn python better. Encryptions and decryptions should be speedy and accurate so im hoping it will improve my programming skills.

I recently wrote this quick script for a shift cypher but i wasnt sure how to be able to define the shift.

import string
m = string.maketrans('abcdefghijklmnopqrstuvwxyz', 'pqrstuvwxyzabcdefghijklmno')

a = 'this should have been fairly easy to crack considering the length of the message'

n = string.maketrans('pqrstuvwxyzabcdefghijklmno', 'abcdefghijklmnopqrstuvwxyz')
x = string.translate(a, m)
print x

y = string.translate(x, n)
print y

for example if i shifter the letter a over 4 times it would be the letter e. I could make 26 encryption variables and 26 decryption variables but this isnt really pythonic or efficient. can anyone point me in the right direction?

Thanks for your time.

[Archenemie]

What if i convert each character to its ASCII value and loop through the ASCII values?

Is this efficient?

[vegaseat]

The deque rotate function might be something to consider ...

# Caesar Cipher encryption/decryption
# using Python's double-ended queue

from collections import deque

def doCaesarCipher(text, shift):
    alpha = 'abcdefghijklmnopqrstuvwxyz'
    dq = deque(alpha)
    # shift/rotate the alphabet (dq in place)
    dq.rotate(shift)
    encrypted = ""
    for c in text.lower():
        if c in alpha:
            index_alpha = alpha.index(c)
            encrypted += dq[index_alpha]
        else:
            encrypted += c
    return encrypted


text = 'pumpkin'
# positive value shifts to the right
# negative value shifts to the left
shift = -5
encrypted = doCaesarCipher(text, shift)

print(text)       # pumpkin
print(encrypted)  # uzrupns

# shift to the right to get original text back
print(doCaesarCipher('uzrupns', 5))  # pumpkin

'abcdefghijklmnopqrstuvwxyz' can be obtained from module string.

[Archenemie]

To be honest thats perfect. I am going to move onto to "polyalphabetic substitution" cyphers and decyphers now. this should help alot :).