for loop result is printed twice-CodePudding

note: the letters are there twice so when shifting a letter at the end of the alphabet i dont get a out of range error

so currently im working on a caesers cypher where you write a word and shift those letters by a certain amount of times

input = abc 
output = bcd

my issue is when the code runs it prints the output letters twice

input = abc
output = bbccdd

heres my code

alphabet = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

direction = input("Type 'encode' to encrypt, type 'decode' to decrypt:\n")
text = input("Type your message:\n").lower()
shift = int(input("Type the shift number:\n"))


def encrypt(text, shift):
    cipher_text = ""
    for i in text:
       for letter in alphabet:
           if i == letter:
               index = alphabet.index(letter)
               shifted_index = index   shift
               shifted_letter = alphabet[shifted_index]
               cipher_text  = shifted_letter
    print(f"The encoded word is {cipher_text}")
encrypt(text, shift)

another example

input = zulu
expected output = avmv
code output = aavvmmvv

CodePudding user response：

Lots of work for what is essentially a one-liner:

import string
alphabet = string.ascii_lowercase   # use the predefined string of lower case letters from the string module
index = {ch: i for i, ch in enumerate(alphabet)}   # pre-calculate the index of each character once.


def encrypt(txt, n):
    return ''.join(alphabet[(index[c]   n) % len(alphabet)] for c in txt)


print(encrypt('spin', 5))

prints

xuns

the modulo operation (ie. ... % len(alphabet)) makes sure the index is within bounds of the alphabet after adding the shift - no matter how big the shift is.

CodePudding user response：

leave it at "for i in text" their is no need for "for letter in alphabet" that is why it is looping through. If that doesnt work take out the duplicates in your alphabet. I didnt notice that on first glance.

CodePudding user response：

As mentioned above, you have the same alphabet twice. So, you need to exit the inner for loop once you have shifted. So, add a break after cipher_text = shifted_letter, that will exit the inner for loop.

Updated Code

alphabet = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

direction = input("Type 'encode' to encrypt, type 'decode' to decrypt:\n")
text = input("Type your message:\n").lower()
#shift = int(input("Type the shift number:\n"))


def encrypt(text, shift):
    cipher_text = ""
    for i in text:
       for letter in alphabet:
           if i == letter:
               index = alphabet.index(letter)
               shifted_index = index   shift
               shifted_letter = alphabet[shifted_index]
               cipher_text  = shifted_letter
               break # NEW LINE
    print(f"The encoded word is {cipher_text}")

shift = int(input("Type the shift number:\n"))
if shift > 26:
    print("Shift should be max 26, exiting...")
else:
    encrypt(text, shift)

Output

Type 'encode' to encrypt, type 'decode' to decrypt:
encode
Type your message:
spin
Type the shift number:
5
The encoded word is xuns

Updated based on feedback

import string

direction = input("Type 'encode' to encrypt, type 'decode' to decrypt:\n")
text = input("Type your message:\n").lower()
shift = int(input("Type the shift number:\n"))

alphabet = string.ascii_lowercase   # use the predefined string of lower case letters from the string module
index = {ch: i for i, ch in enumerate(alphabet)}   # pre-calculate the index of each character once.

def encrypt(txt, n):
    return ''.join(alphabet[(index[c]   n) % len(alphabet)] for c in txt)

encrypt(text, shift)

Output

Type 'encode' to encrypt, type 'decode' to decrypt:
encode
Type your message:
xylophone
Type the shift number:
100
'tuhkldkja'

CodePudding user response：

Remove the inner for loop and the if and then find the first index of the current character in the alphabet.

def encrypt(text, shift):
    cipher_text = ""
    for i in text:
        index = alphabet.index(i)
        shifted_index = index   shift
        shifted_letter = alphabet[shifted_index]
        cipher_text  = shifted_letter
    print(f"The encoded word is {cipher_text}")

This code sticks closely to your approach. There are better solutions, like the one from @thebjorn.