Why is my iteration not working inside the function?

Question

#Password Checker Program
def lengthCheck(pWord):
    if len(pWord) >= 6 and len(pWord) <= 12:
        return True
    else:
        return False

def checkUpper(pWord):
    for letters in pWord: #Why is my iteration not working?
        upperLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        if upperLetters in pWord:
            return True
        else:
            return False

def checkLower(pWord):
    for letters in pWord: #Why is my iteration not working?
        upperLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        lowerLetters = upperLetters.lower()
        if lowerLetters in pWord:
            return True
        else:
            return False

def checkDigit(pWord):
    for letters in pWord: #Why is my iteration not working?
        digitNumbers = "0123456789"
        if digitNumbers in pWord:
            return True
        else:
            return False

def complexCheck(pWord):
    if checkUpper(pWord) and checkLower(pWord) and checkDigit(pWord):
        return True
    else:
        return False

def passCheck(pWord):
    if lengthCheck(pWord) and complexCheck(pWord):
        return True
    else:
        return False

goodPWord = True
pWord = ""
pWord = input("Please enter your password: ")
goodPWord = passCheck(pWord)
if goodPWord:
    print(pWord, " is a good password.")
else:
    print(pWord, " is not a good password")

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Answer 1

I'll focus on checkUpper and then you can replicate in the other two functions.

You have two main problems.

The first problem is that you're trying to match the entire string of upperLetters to see if it exists in pWord, even though you're looping pWord. Instead, you need to check if the currently looped letter is inside upperLetters.

This:

if upperLetters in pWord:

Should be this instead:

if letters in upperLetters:

You're looping pWord and getting a letter at a time (which you called letters). That's what you need to compare to upperLetters, not the whole pWord.

The second problem is that you're returning true or false after the first check so if the first letter isn't an uppercase letter then the rest of the password is ignored! Instead you need to keep a boolean variable that is returned false only if none of the letters match upperLetters.

So the whole function becomes this:

def checkUpper(pWord):
    upperLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" #Moved here so you don't define it on every iteration of the loop
    atLeastOne = False #Start as false
    for letters in pWord: #Loop through all letters
        if letters in upperLetters: #Does the current letter exist in upperLetters?
            atLeastOne = True #If so the flag becomes True
            break #exit the loop
    return atLeastOne #Returns false only if none of the letters were upper case

You can also avoid the flag entirely (as below), but I think the above is clearer to read and understand, and would be more useful if in the future you want to check if they have more than 1 upper case letter, for example, by keeping a counter instead of a boolean.

def checkUpper(pWord):
    upperLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" #Moved here so you don't define it on every iteration of the loop
    for letters in pWord: #Loop through all letters
        if letters in upperLetters: #Does the current letter exist in upperLetters?
            return True
    return False #If none matched

Just replicate these changes to the remaining functions.