February Python Challenge

1. Using the code below recreate the Caesar Cipher in Python
2. Add comments describing what each section does.
3. Test the cipher to ensure that it is working
4. Report your results in a word processed document with the following headings:


Introduction

-State user requirements for the Caesar cipher

Annotated Code

Output


N.B. You may use your own code if you wish but needs to have the same user requirements as the one below.  You may need to look at this code to work them out

DEADLINE MARCH 10th

def caesar_cipher(message, key, action):
    letters = ['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',
                '1', '2', '3', '4', '5', '6', '7', '8', '9']
    
    number_in_list = len(letters)
    output_message = ""
    for next_character in message:
        in_list = False
        i = 0
        while i < number_in_list:
            new_position = 0
            if next_character == letters[i]:
                in_list = True
                # What happens next determined by value of action.
                if action == 'E':
                    new_position = i + key
                else:
                    new_position = i - key                   
                if new_position >= number_in_list:
                    new_position -= number_in_list
                output_char = letters[new_position]
            i += 1
        if in_list:
             output_message += output_char
        else:
            output_message += next_character
    return output_message

   
#Main program
print("CAESAR CIPHER")
print("")
print("OPTIONS")
print("")
flag = True
while flag:
    print("")
    print("1. Encrypt a message")
    print("2. Decrypt a message")
    print("3. Exit the program")
    answer = input("Please select an option. ")
    if answer == "1":
        message = input("Enter the message you want to encrypt: ")
        key = input("Enter the key: ")
        action = "E"
        print("The encoded message is: ")
        print(caesar_cipher(message, int(key), action))
    elif answer == "2":
        message = input("Enter the message you want to decrypt: ")
        key = input("Enter the key: ")
        action = "D"
        print("The decoded message is: "),
        print(caesar_cipher(message, int(key), action))
    elif answer =="3":
        flag = False

print("Good bye")