I have an error, but I am not figuring out what is causing it

Question

I am taking a previously written caesar cipher and adding it to a vigenere cipher. I am getting a NameError code and do not know how to resolve it

def alphabet_position(letter):
    alphabet_pos = {'A':0, 'a':0, 'B':1, 'b':1, 'C':2, 'c':2, 'D':3,
                    'd':3, 'E':4, 'e':4, 'F':5, 'f':5, 'G':6, 'g':6,
                    'H':7, 'h':7, 'I':8, 'i':8, 'J':9, 'j':9, 'K':10,
                    'k':10, 'L':11, 'l':11, 'M':12, 'm':12, 'N': 13,
                    'n':13, 'O':14, 'o':14, 'P':15, 'p':15, 'Q':16,
                    'q':16, 'R':17, 'r':17, 'S':18, 's':18, 'T':19,
                    't':19, 'U':20, 'u':20, 'V':21, 'v':21, 'W':22,
                    'w':22, 'X':23, 'x':23, 'Y':24, 'y':24, 'Z':25, 'z':25 }
    pos = alphabet_pos[letter]
    return pos


def rotate(letter, rot):
    shift = 97 if letter.islower() else 65
    return chr((ord(letter) + rot - shift) % 26 + shift)

def vigenere(msg, rot):
    list1 = ""
    for char in msg:
        list1 += rotate(letter, rot)
    return list1

def main():
    letter = input('Enter a letter: ')
    rot = int(input('Enter a number: '))
    print(alphabet_position(letter))
    print(rotate(letter,rot))
    x = input("Type a message: ")
    y = input("Rotate by: ")
    result = vigenere(x, y)
    print (result)

if __name__ == '__main__':
    main()

My error is: NameError: name 'letter' is not defined on line 21

I thought it should pull from the correct function so the letter should be defined?

Answer 1

In the vigenere function, change list1 += rotate(letter, rot) to list1 += rotate(char, rot) - there is no letter variable declared in that function.

As an aside, make sure your indenting is correct: your def main() appears to be indented incorrectly.

Answer 2

Yes, it is not defined indeed:

def vigenere(msg, rot):
    list1 = ""
    for char in msg:
        list1 += rotate(char, rot)  #<-- change to char
    return list1