TypeError: string indices must be integers inpython

Question

here is my code:

import time

ed = input('Encrypt (e) or decrypt (d)? ')

chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ "
charsLen = len(chars)

def numberToStr(num):
    s = ""
    while num:
        s = chars[num % charsLen] + s
        num //= charsLen

    return(s)
def strToNumber(numStr):
    num = 0
    for i, c in enumerate(reversed(numStr)):
        num += chars.index(c) * (charsLen ** i)

    return(num)

def enc():
    key = input('What is your key? (Alphanumeric and space) ')
    ID = int(input('What is your ID? (0-9, 3+ digits) '))
    inp = int(strToNumber(input('What do you want to encrypt? ')))
    keyAsNum = int(strToNumber(key))
    enc.asint = inp ** 2
    enc.asint = enc.asint * ID
    enc.asint = enc.asint - keyAsNum
    enc.astext = numberToStr(int(enc.asint))
    return(enc)


def dec():
    key = input('What is your key? (Alphanumeric and space) ')
    ID = int(input('What is your ID? (0-9, 3+ digits) '))
    inp = int(strToNumber(input('What do you want to decrypt? ')))
    keyAsNum = int(strToNumber(key))
    message = inp + keyAsNum
    message = message // ID
    message = math.sqrt(message)
    message = numberToStr(message)
    return(message)

if ed=='e':
    crypt = enc()
    print('crypt.asint:\n' + str(crypt.asint) + '\ncrypt.astext:\n' + crypt.astext)
elif ed=='d':
    crypt = dec()
    print(crypt)

time.sleep(10)

and here is the error: File "stdin", line 5, in module

File "stdin", line 9, in dec

File "stdin", line 4, in numberToStr

TypeError: string indices must be integers

I cannot figure out why it is throwing this error and cannot find anything on google.

Answer 1

The traceback tells you exactly what is wrong. You are doing

s = chars[num % charsLen] + s

but you don't know for sure that num is an int because, previously, you do:

message = math.sqrt(message)
message = numberToStr(message)

What type does math.sqrt return?

Answer 2

Well, I am a little bit confused by how you're using the square root function. When I run this:

from math import sqrt
type(sqrt(7)) #I want to recognize the type of what sqrt returns

it returns:

<class 'float'>

So that makes sense if you're trying to index your chars using a non-int value.