Define variable in while loop

Question

I going through a python course and am stuck at trying to use a while loop properly in my code

My code is supposed to check a password if it has min length =6 and max length =14, it will also check if the password only has numbers or letters. If it has a combination of both its supposed to print "strong password" if it only has numbers or letters it will print "weak password".

MIN_PASSWORD_LENGTH = 6

MAX_PASSWORD_LENGTH = 14


while password_length >= MIN_PASSWORD_LENGTH or password_length <= MAX_PASSWORD_LENGTH:

password_length = len(password)

password = input("Enter your password: ")


if password.isalpha():

    print("Your password is weak!")

elif password.isnumeric():

    print("Your password is weak!")

else:

    print("Your password is strong!")


print("Number of characters used in password: ", password_length,"the min length expected is: ",MIN_PASSWORD_LENGTH,
"the max length is: ", MAX_PASSWORD_LENGTH)

When I run my code, it comes with error message: 'name password_length is not defined'. I am not sure what to do? Is my code even correct? Am I supposed to put the password_length outside the while loop?

The code block could use indentations. (*Hint hint: you're using password_length before you're defining it.) — TrebledJ, Mar 25 '19 at 01:11
Also suggest you read [Asking the user for input until they give a valid response](https://stackoverflow.com/questions/23294658/asking-the-user-for-input-until-they-give-a-valid-response). — martineau, Mar 25 '19 at 02:20

score 1 · Answer 1 · answered Mar 25 '19 at 01:19

You have, more or less, the right idea. It's just that you need to assign a value to password_length outside your loop.

Think about this: when your code is run, the interpreter hits the while loop and attempts to make a comparison involving password_length. However, at that point password_length doesn't exist yet, since the first time it gets a value is inside the loop. Therefore, you should initialise it to a sensible value, such as 0, before entering the loop.

Two supplementary points:

You're calculating the password length of the previous password, so if you enter a too-short/long password and then an acceptable one, the length printed will be of the unacceptable one.
In general, prefer f-strings or str.format calls to string concatenation, so, for your print, this might be better:

print(f'Number of characters used in password: {password_length}; '
       'the min length expected is {MIN_PASSWORD_LENGTH} and the '
       'max length expected is {MAX_PASSWORD_LENGTH}.')

score 1 · Answer 2 · answered Mar 25 '19 at 01:20

Immediately before the while loop, initialize with something like "password_length = MAX_PASSWORD_LENGTH" or else the while loop cannot start. The first line inside the while loop is "password_length = len(password)", which will set the value of password_length correctly, but the while loop needs something to start with so that you can reach that point.

Pablo · Answer 3 · 2019-03-25T01:34:43.880

Conditions in the while loop are wrong. You may try:

MIN_PASSWORD_LENGTH = 6

MAX_PASSWORD_LENGTH = 14

password = input("Enter your password: ")
password_length = len(password)

while password_length < MIN_PASSWORD_LENGTH or password_length > MAX_PASSWORD_LENGTH:
    print("Password length", password_length, "incorrect. Required between", MIN_PASSWORD_LENGTH, "and", MAX_PASSWORD_LENGTH)
    password = input("Enter your password again: ")
    password_length = len(password)

if password.isalpha() or password.isnumeric():
    print("Your password is weak!")
else:
    print("Your password is strong!")

print("Number of characters used in password:", password_length,". The min length expected is:",MIN_PASSWORD_LENGTH, ". The max length is: ", MAX_PASSWORD_LENGTH)

Axifive · Answer 4 · 2019-03-25T01:30:32.970

You're using password and password_length variables before they are defined.

Also you can use function and rewrite it more structured:

MIN_PASSWORD_LENGTH = 6
MAX_PASSWORD_LENGTH = 14

def checkPass():
    password = input("Enter your password: ")
    password_length = len(password)

    if password.isalpha():
        print("Your password is weak!")
    elif password.isnumeric():
        print("Your password is weak!")
    else:
        print("Your password is strong!")

    return password_length >= MIN_PASSWORD_LENGTH or password_length <= MAX_PASSWORD_LENGTH

while checkPass():
    continue

print("Number of characters used in password: ", password_length,"the min length expected is: ",MIN_PASSWORD_LENGTH, "the max length is: ", MAX_PASSWORD_LENGTH)

Online demo

score 1 · Answer 5 · answered Mar 25 '19 at 01:24

The problem is your calling password before the code knows what it is.

MIN_PASSWORD_LENGTH = 6

MAX_PASSWORD_LENGTH = 14

# password must be defined before you use it. 
password = input("Enter your password: ")

while password_length >= MIN_PASSWORD_LENGTH or password_length <= MAX_PASSWORD_LENGTH:

password_length = len(password)  

if password.isalpha(): 
    print("Your password is weak!")

elif password.isnumeric(): 
    print("Your password is weak!")

else: 
    print("Your password is strong!")   

print("Number of characters used in password: ", password_length,"the min length expected is: ",MIN_PASSWORD_LENGTH,
"the max length is: ", MAX_PASSWORD_LENGTH)

score 1 · Answer 6 · answered Mar 25 '19 at 01:31

Here is a version based on what I understood

MIN_PASSWORD_LENGTH = 6
MAX_PASSWORD_LENGTH = 14
password = ""
atLeast1Apha = False
atLeast1Numeric = False

while True:
    password = input("Enter your password: ")   
    if len(password) > MAX_PASSWORD_LENGTH or len(password) < MIN_PASSWORD_LENGTH:
        print("Password could be between %s and %s long" %(MIN_PASSWORD_LENGTH, MAX_PASSWORD_LENGTH))
        continue
    for char in password:
        if char.isalpha():
            atLeast1Apha = True
        if char.isdigit():    
            atLeast1Numeric = True
    break        

if atLeast1Apha and atLeast1Numeric:
    print("Your password is strong!")
else:
    print("Your password is weak!")

Define variable in while loop

6 Answers6