Encryption of an input with Caesar Cipher in Python

Question

I have to write this code where The function must receive a path to a text file which must contain text composed of only English letters and punctuation symbols and a destination file for encrypted data. Punctuation symbols must be left as they are without any modification and the encrypted text must be written to a different file.
Also, I have to validate the inputs.

I’ve done most of it but in the first part, where I have to ask for a text, the code isn’t accepting spaces or punctuation marks, and as I gather it’s because of .isalpha, however I couldn’t find a way to fix it.

I’m not sure if I have completed the aforementioned requirements, so any type of feedback / constructive criticism is appreciated.

  while True:   #  Validating input text
    string = input("Enter the text to be encrypted: ")
    if not string.isalpha():
        print("Please enter a valid text")
        continue
    else:
        break
while True:  #  Validating input key
    key = input("Enter the key: ")
    try:
        key = int(key)
    except ValueError:
        print("Please enter a valid key: ")
        continue
    break


def caesarcipher(string, key):   #  Caesar Cipher
    encrypted_string = []
    new_key = key % 26
    for letter in string:
        encrypted_string.append(getnewletter(letter, new_key))
    return ''.join(encrypted_string)


def getnewletter(letter, key):
    new_letter = ord(letter) + key
    return chr(new_letter) if new_letter <= 122 else chr(96 + new_letter % 122)


with open('Caesar.txt', 'a') as the_file:  # Writing to a text file
    the_file.write(caesarcipher(string, key))

print(caesarcipher(string, key))
print('Your text has been encrypted via Caesar-Cipher, the result is in Caesar.txt')

Asked By: Juj

||

Source

Answer 1

Well, you could check it "manualy".

# ____help_function____
def check_alpha(m_string):
   list_wanted = ['!', '?', '.', ',']

   for letter in m_string:
      if not (letter in list_wanted or letter.isalpha()):
         return False

   return True

# ____in your code____
while True:
   string = input("Enter the text to be encrypted: ")

   if check_aplha(string):
      break
   else:
      print('....')

Answered By: JohnyCapo

Answer 2

You can validate input string by checking if it doesn’t contain any Alphabet characters then it’s invalid input:

import string

def check_valid_input(str):
    for c in str:
        if not c.isalpha() and (c not in string.punctuation):
            return False
    return True and any(c.isalpha() for c in str)
     

while True:   #  Validating input text
    string = input("Enter the text to be encrypted: ")
    # checking if contain only alphabet characters and punctuations
    if not check_valid_input(string): 
        print("Please enter a valid text")
        continue
    else:
        break

In this way you only accept input string if there are alphabet characters and doesn’t contain any special characters(other than punctuation) in it.

Answered By: Oghli

Encryption of an input with Caesar Cipher in Python

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