find ( letter ) - key ) % len ( alpha ) result = result + get_cipherletter ( new_key, letter ) return result upper () alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" result = "" for letter in message : new_key = ( alpha. find ( letter ) + key ) % len ( alpha ) result = result + get_cipherletter ( new_key, letter ) return result def decrypt ( key, message ): message = mesage.
#Caesar cipher decryption tool code#
Next, we remove the bits of code from our encrypt and decrypt functions that are now redundant and replace it with code that uses the function:ĭef get_cipherletter ( new_key, letter ): #still need alpha to find letters alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" if letter in alpha : return alpha else : return letter def encrypt ( key, message ): message = mesage. find ( letter ) - key ) % len ( alpha ) result = result + alpha else : result = result + letter return result upper () alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" result = "" for letter in message : if letter in alpha : #if the letter is actually a letter #find the corresponding ciphertext letter in the alphabet letter_index = ( alpha. find ( letter ) + key ) % len ( alpha ) result = result + alpha else : result = result + letter return result def decrypt ( key, message ): message = mesage. We can know that this works for loop-arounds by observing the following behavior:ĭef get_cipherletter ( new_key, letter ): #still need alpha to find letters alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" if letter in alpha : return alpha else : return letter def encrypt ( key, message ): message = mesage. This works because any number that is greater than 26 will be reduced to a number from 0 to 25, since the remainder of anything divided by 26 can only be from 0-25. We can use modulo to handle loop-arounds. This is a prime example of where modulo would be helpful. While we could use an if statement for this, there exists a better way.
The consistent thing here is that if our index is 26 or over, we want to subtract 26. If our index goes to 28, we want our index to actually be 2. We forgot to handle loop-arounds! How do we handle what happens when we reach the end of the alphabet? Well, whenever we hit a index of 26, we want that index to becomes zero (especially since alpha doesn’t have a 26th index!). find ( letter ) + key result = result + alpha else : result = result + letter
upper () alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" result = "" for letter in message : if letter in alpha : #if the letter is actually a letter #find the corresponding ciphertext letter in the alphabet letter_index = alpha. Def encrypt ( key, message ): message = mesage.
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