Vigenere cipher in python

Question

Writing a vigenere cipher in python and I've got completely lost in it, anyone fancy giving me a hand and suggesting things that could be improved/make it work correctly? Currently I'm getting all sorts of errors

letters='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
print ("This program will take a keyword, and use it to encrypt plaintext.")
def keyword():
    print ("Please enter your keyword")
    keyword = input()
    return keyword

def plaintext():
    print ("Please enter your plaintext")
    plaintext = input()
    return plaintext

def translate (keyword, plaintext):
    keywordtwo=0
    number=0
    keyword=keyword.upper()
    length = len(plaintext)
    lengthtwo=len(keyword)
    for symbol in plaintext:
        number=letters.find(symbol.upper())
        if number!=-1:
            number+=letters.find
        num%=len(letters)
        if symbol.isupper():
            translated.append(letters[number])
        elif symbol.islower():
            translated.append(letters[number].lower())
        if keywordtwo==len(keyword):
           keywordtwo=0
    else:
        translated.append(symbol)
    return ' '.join(translated)




keyword = keyword()
plaintext = plaintext()
translated = translate(keyword, plaintext)

print ("Your new text is:")
print (translate(keyword, plaintext))

TypeError: unsupported operand type(s) for +=: 'int' and 'builtin_function_or_method' is the most recent one @PieterWitvoet — bleh, Dec 11 '14 at 09:48
number+=letters.find doesn't seem correct, you have to pass an argument to find — Mathieu Borderé, Dec 11 '14 at 09:53
It might also be worth reading up on some literature to improve your coding style. Your program is messy and difficult to understand for the reader. This is an extremely important skill to master and is best learned sooner rather than later. — Mathieu Borderé, Dec 11 '14 at 10:13

Pieter Witvoet · Answer 1 · 2014-12-11T10:02:51.517

TypeError: unsupported operand type(s) for +=: 'int' and 'builtin_function_or_method' refers to the code at line 22: number+=letters.find.

number is an int (number) and letters.find is a method (a built-in method), and you're trying to add those together. That's not going to work. What you probably intended to do was to call that function, which looks like number += letters.find(...), where ... stands for whatever letter you want to look up.

The next error you'll get will be something like UnboundLocalError: local variable 'num' referenced before assignment. That's on line 23: number%=len(letters). num does not exist, I assume you meant number instead.

Then you'll get NameError: global name 'translated' is not defined, which refers to line 31: translated.append(symbol). You're trying to add an item to a list named translated, but translated does not exist at that point (you do define it further down, outside your translate function, but even then, you should use a local variable, not a global one). Add translated = [] to the start of your translate function.

Vigenere cipher in python

1 Answers1