Python cipher program - Too many members

Question

I'm currently trying to make a cipher program, here is my code;

import string
import random

matrix = []
codedmessage = []
letter = "ABCDEF"

message = input("Enter message to be encoded:\n").upper().replace(' ', '')
print ('---MESSAGE---\n', message)

newlist = list(string.ascii_uppercase + string.digits)
random.shuffle(newlist)

print ('---MATRIX---')

for x in range(0,len(newlist),6):
    matrix.append(list(newlist[x:x+6]))

for letter in message: 
   for y, vector in matrix: 
      for s, member in vector: 
          if letter == member:
            codedmessage.append(letter[x], letter[y])

for i in range(len(matrix)):
    print(matrix[i])

However, when I compile this I get the error;

for y, vector in matrix: ValueError: too many values to unpack (expected 2)

Can anyone shed some light on this as to why it is happening and give a solution?

Thanks

Answer 1

matrix.append(list(newlist[x:x+6]))

You append 6 element lists to matrix, but you try to unpack them into two variables later:

for y, vector in matrix:

The numbers have to match.

Currently you matrix looks like [ [4,3,2,6,3,2], [2,1,6,8,9,2], ... ]. How is python supposed to unpack one of the elements, for example [4,3,2,6,3,2] into y and vector? What should go where? (For possible solutions see the other answers, they were faster. I don't understand what behaviour is expected anyway.)

Also you cannot index a character:

codedmessage.append(letter[x], letter[y])

previously you assigned a single character to letter, here:

for letter in message: 

because message is a string. You probably confuse names as you already have assigned a string to letter initially: letter = "ABCDEF" Probably you want to use two different names.

append does only take one argument, too. Again I don't know what you expect, but I guess it should be either codedmessage.append([letter[x], letter[y]]) or codedmessage += [letter[x], letter[y]].

I also highly doubt that you want to use x in codedmessage.append(letter[x], letter[y]) because you only used x in another independent loop as iteration variable.

Answer 2

Each element of matrix is a list of six items, so if you only provide two variable names on the left-hand side, Python doesn't know what to do with the other four.

However, you can (in Python 3) unpack back into a list like this:

>>> a, *b = [1,2,3,4,5,6]
>>> a
1
>>> b
[2, 3, 4, 5, 6]