Index Error in python
encryption, python
Solution
In your while condition, you are ensuring that `i < len(BinKey)`. This means that `BinKey[i]` will be valid, but `BinKey[i+1]` will not be valid at the last iteration of your loop, as you will then be accessing `BinKey[len(BinKey)]`, which is one past the end of your string. Strings in python start at `0` and end at `len-1` inclusive.
To avoid this, you can update your loop criterion to be
while BinKeyLength > i+1 and ...:
Problem
I am new to programming, and I am trying to write a Vigenère Encryption Cipher using python. The idea is very simple and so is my function, however in this line: ``` ( if((BinKey[i] == 'b')or(BinKey[i+1] == 'b')): ) ``` It seems that I have an index problem, and I can't figure out how to fix it. The error message is: ``` IndexError: string index out of range ``` I tried to replace the `i+1` index by another variable equal to `i+1`, since I thought that maybe python is re-incrementing the `i`, but it still won't work. So my questions are: How to fix the problem, and what have I done wrong? Looking at my code, what can I learn to improve my programming skills? I want to build a simple interface to my program (which will contain all the encryption ciphers), and all I came up with from Google is pyqt, but it just seems too much work for a very simple interface, so is there a simpler way to build an interface? (I am working with Eclipse Indigo and pydev with Python3.x) The Vigenère Encryption function (which contains the line that causes the problem) is: ``` def Viegner_Encyption_Cipher(Key,String): EncryptedMessage = "" i = 0 j = 0 BinKey = Bin_It(Key) BinString = Bin_It(String) BinKeyLengh = len(BinKey) BinStringLengh = len(BinString) while ((BinKeyLengh > i) and (BinStringLengh > j)): if((BinKey[i] == 'b')or(BinKey[i+1] == 'b')): EncryptedMessage = EncryptedMessage + BinKey[i] else: EncryptedMessage = EncryptedMessage + Xor(BinKey[i],BinString[j]) i = i + 1 j = j + 1 if (i == BinKeyLengh): i = i+j return EncryptedMessage ``` This is the `Bin_It` function: ``` def Bin_It(String): TheBin = "" for Charactere in String: TheBin = TheBin + bin(ord(Charactere)) return TheBin ``` And finally this is the `Xor` function: ``` def Xor(a,b): xor = (int(a) and not int(b)) or (not int(a) and int(b)) if xor: return chr(1) else: return chr(0) ```