Python 2 Caesar Cipher

Question

My question is how to improve the code so that it can adapt to however long the input message is. As is, the message must be 5 letters. I would like to improve the code such that a message of any length can be inputted and the cipher will work with it. Help would be much appreciated. :-) See the code below!

#Enter your message
message=raw_input('Enter your message here. Make sure to use all CAPS througout your message and leave no spaces in between words.')
length=len(message)
print 'The length of your message is ',length
#This statement is a possible idea to let the program know how many letters it will be need to shift. But I don't know how to actually do this.
print chr(length+64)
#Indexes letters out of message.
A=message[length-length]
B=message[length-length+1]
C=message[length-length+2]
D=message[length-length+3]
E=message[length-length+4]
#Shifts letters and accounts for shifting XYZ to ABC. 
def shift(x):
 if ord(x)+3==91:
 return 65
 if ord(x)+3==92:
 return 66
 if ord(x)+3==93:
 return 67
 else:
 return ord(x)+3
a2=shift(A)
b2=shift(B)
c2=shift(C)
d2=shift(D)
e2=shift(E)
#Converts shifted ordinals back to characters
def convert(x):
 return chr(x)
first=convert(a2)
second=convert(b2)
third=convert(c2)
fourth=convert(d2)
fifth=convert(e2)
#Prints resultant characters
print first,second,third,fourth,fifth

• jonrsharpe: Read about lists and loops (start here).

Answer 1

import string
shift_amt = 13
alphabet_lc = string.ascii_lowercase
shifted_lc = alphabet_lc[shift_amt:]+alphabet_lc[:shift_amt]
alphabet_uc = alphabet_lc.upper() 
shifted_uc = shifted_lc.upper()
trans_tab = string.maketrans(alphabet_lc+alphabet_uc,shifted_lc+shifted_uc)
message = "Encode Me To a new MessaGez!"
print message.translate(trans_tab)

is one way of doing it in Python2 at least

Answer 2

Use two for loops, one for looping through each character, and one for shifting the character the desired amount of times. We use a function upper() to shift a character.

def upper(char):
 from string import ascii_letters as _all
 if char == ' ':
 return ' '
 return _all[_all.index(char)+1] if char != 'Z' else 'a'
def shift(message, key):
 temp = []
 for i in message:
 char = i
 for k in range(key):
 char = upper(char)
 temp.append(char)
 return ''.join(temp)
message=raw_input('Enter your message here: ')
key = int(raw_input('Enter the desired key: '))
length=len(message)
print 'The length of your message is', length
print 'Your encrypted message is {0}'.format(shift(message, key))

This runs as:

bash-3.2$ python caesar.py
Enter your message here: This works WITH or without CAPS
Enter the desired key: 10
The length of your message is 31
Your encrypted message is drsC GyBuC gSdR yB GsDryED MKZc
bash-3.2$ 

Answer 3

The Ceasar cipher is built in in python 2;

In [6]: 'The Caesar cipher is built-in.'.encode('rot13')
Out[6]: 'Gur Pnrfne pvcure vf ohvyg-va.'

As you can see, this encoding only acts on letters, and it works for upper and lower case.

But is you want to remove spaces and make every thing upper-case, Python can do that as well;

In [9]: 'this is a string'.translate(None, ' \t')
Out[9]: 'thisisastring'
In [10]: 'this is a string'.translate(None, ' \t').upper()
Out[10]: 'THISISASTRING'
In [11]: 'this is a string'.translate(None, ' \t').upper().encode('rot13')
Out[11]: 'GUVFVFNFGEVAT'

Or in a different way;

In [15]: ''.join('this is a string'.split()).upper().encode('rot13')
Out[15]: 'GUVFVFNFGEVAT'

Answer 4

Here is a simple Caesar cipher program written for Python 3 that should not be very difficult to rewrite for Python 2:

import string
def main():
 key = 5
 table = str.maketrans(string.ascii_letters,
 string.ascii_lowercase[key:] +
 string.ascii_lowercase[:key] +
 string.ascii_uppercase[key:] +
 string.ascii_uppercase[:key])
 plaintext = input('Please enter a phrase: ')
 ciphertext = plaintext.translate(table)
 print('Your encrypted phrase is:', ciphertext)
if __name__ == '__main__':
 main()

• Artjom B.: Please don't copy your answer for the caesar cipher on every question that you find. Instead engange in a unique answer for every question.