"IndexError: string index out of range" error, despite no flaws in code

Question

I am making a registration module for a Python Quiz which I am developing, solely to improve my programming technique. Here is my code:

def quiz():
    print('success')
def loginPage():
    fr=open("ddddfile.txt",'r').read()
    v=False
    while v==False:
        un=input('Please enter your username.')
        pw=input('Please enter your password.')
        v2=0
        print(fr[v2][2], fr[v2][3])
        if fr[v2][3]==un and fr[v2][4]==pw:
            print('Successfully logged in.')
            v=True
            quiz()
        else:
            print('Incorrect username or password. Please try again.')
            v2+=1

def registerPage():                                               
    v=0                                                                     
    while v<3:                                                  
        n=input('Please enter your name.')                         
        if n==str(n):                                      
            v+=1                                                   
        a=input('Please enter your age.')                           
        if int(a)>10 and int(a)<20:                               
            v+=1                                                    
        yg=input('Please enter your year group.')        
        if int(yg)>6 and int(yg)<15:                              
            v+=1                                            
    un=n[:3]+a                                               
    print('Your new username is', un, '. Please remember this as you will need it to log in.')
    v=False                                                  
    while v==False:                                         
        pw=input('Please enter your desired password.')       
        pwc=input('Please re-enter your password.')
        if pw==pwc:
            v=True
    usrInf=[n,a,yg,un,pw]
    fw=open("ddddfile.txt",'r+')
    fw.write(',')
    fw.writelines(str(usrInf))
    fw.close()
    loginPage()

def startPage():
    c1=input('Welcome to the Quiz. Please type "login" or "register".')
    v=False
    while v==False:
        if c1.lower()=='login' or c1.lower()=='l':
            v=True
            loginPage()
        elif c1.lower()=='register' or c1.lower()=='r':
            v=True
            registerPage()
        else:
            c1=input('Please type "login" or "register".')
startPage()

As you can see, I am storing user data in an external text file. The contents of the text file is as follows:

[['Xavier Pamment', '16', '11', 'Xav16', 'nL4WVba2KR'],[]]

However, in the loginPage() function, when run, once the code tries to validate the user inputted details, I get this error:

Traceback (most recent call last):
File "C:\Users\xavier\Desktop\dddd.py", line 58, in <module>
    startPage()
File "C:\Users\xavier\Desktop\dddd.py", line 52, in startPage
    loginPage()
File "C:\Users\xavier\Desktop\dddd.py", line 10, in loginPage
    print(fr[v2][2], fr[v2][3])
IndexError: string index out of range

Does anyone know where I have slipped up? Thanks, CH

Answer 1

When you do fr=open("ddddfile.txt",'r').read(), you are getting the contents of the file in the form of a string. You need to convert that string into a list before trying to index it in the way that you are. You should look into ast.literal_eval.